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Abstract:

An illumination optical system illuminates an irradiated surface with
light supplied from a light source. The illumination optical system
includes a diffractive optical element disposed in an optical path of
linearly polarized light supplied from the light source. The diffractive
optical element forms a multipole illumination field. including a
plurality of illumination fields. The illumination optical system also
includes an optical integrator that forms a multipole light source
including a plurality of planar light sources with light that has passed
through the multipole illumination field. The illumination optical system
also includes a polarization optical member disposed in an illumination
optical path and that sets a polarization direction of light that has
passed through the multipole light source to a predetermined polarization
direction.

Claims:

1. An illumination optical system that illuminates an irradiated surface
with light supplied from a light source, the illumination optical system
comprising: a diffractive optical element disposed in an optical path of
linearly polarized light supplied from the light source and that forms a
multipole illumination field including a plurality of illumination
fields; an optical integrator that forms a multipole light source
including a plurality of planar light sources with light that has passed
through the multipole illumination field; and a polarization optical
member disposed in an illumination optical path and that sets a
polarization direction of light that has passed through the multipole
light source to a predetermined polarization direction.

2. The illumination optical system according to claim 1, wherein the
diffractive optical element forms two illumination fields aligned along a
first direction crossing an optical axis of the illumination optical
system.

3. The illumination optical system according to claim 2, wherein the
polarization optical member sets the predetermined polarization direction
to a second direction perpendicular to the first direction.

4. The illumination optical system according to claim 3, wherein the
diffractive optical element is interchangeable with a second diffractive
optical element that forms two illumination fields aligned along the
second direction.

5. The illumination optical system according to claim , wherein when the
second diffractive optical element is set in the illumination optical
path, the polarization optical member sets the predetermined polarization
direction to the first direction.

6. The illumination optical system according to claim 1, wherein the
polarization optical member includes a phase member that is arranged in
the optical path of the illumination optical system and that rotates the
polarization direction of the linearly polarized light about an optical
axis of the illumination optical system.

7. The illumination optical system according to claim 6, wherein the
phase member is a 1/2 wavelength plate, which is rotatable about the
optical axis.

8. The illumination optical system according to claim 6, wherein the
polarization optical member includes a second phase member, which is
arranged closer to the light source than the phase member in the optical
path of the illumination optical system and that changes an elliptical
degree of the polarized light emitted by the polarization optical member.

9. The illumination optical system according to claim 8, wherein the
second phase member includes a 1/4 wavelength plate, which is rotatable
about the optical axis.

10. The illumination optical system according to claim 1, wherein the
illumination optical system is used in an exposure apparatus while a mask
and a substrate are being moved in a scan direction, and the substrate is
exposed via a projection optical system; and the predetermined
polarization direction is the scan direction or a direction perpendicular
to the scan direction.

11. The illumination optical system according to claim 1, wherein the
multipole illumination field and light source are dipole or quadrupole.

12. The illumination optical system according to claim 1, further
comprising: a depolarizer that is selectively positioned in the optical
path of the illumination optical system.

13. The illumination optical system according to claim 1, wherein the
linearly polarized light supplied from the light source has a
polarization degree of 95% or more.

14. A method of illuminating an irradiated surface with light supplied
from a light source, the method comprising: diffracting linearly
polarized light from the light source to form a multipole illumination
field including a plurality of illumination fields; forming a multipole
light source including a plurality of planar light sources with light
that has passed through the multipole illumination field; and setting a
polarization direction of light that has passed through the multipole
light source to a predetermined polarization direction.

15. The illumination method according to claim 14, wherein forming the
multipole illumination field includes forming two illumination fields
aligned along a first direction crossing an optical axis of an
illumination optical system that performs the method.

16. The illumination method according to claim 15, wherein the
predetermined polarization direction is set to a second direction
perpendicular to the first direction.

17. The illumination method according to claim 16, wherein forming the
multipole illumination field includes forming two illumination fields
aligned along the second direction, instead of forming the two
illumination fields aligned along the first direction.

18. The illumination method according to claim 17, wherein when the two
illumination fields aligned along the second direction are formed, the
predetermined polarization direction is set to the first direction.

19. The illumination method according to claim 14, wherein setting the
polarization direction to the predetermined polarization direction
includes rotating the polarization direction of the linearly polarized
light about an optical axis of an illumination optical system that
performs the method.

20. The illumination method according to claim 19, wherein setting the
polarization direction to the predetermined polarization direction
includes changing an elliptical degree of polarized light that is
emitted, and the polarization direction of the linearly polarized light
about the optical axis of the illumination optical system is rotated
subsequent to changing the elliptical degree.

21. The illumination method according to claim 14, wherein the
illumination method is used in an exposure process while a mask and a
substrate are being moved in a scan direction, and the substrate is
exposed via a projection optical system; and the predetermined
polarization direction is the scan direction or a direction perpendicular
to the scan direction.

22. The illumination method according to claim 14, wherein the multipole
illumination field and light source are dipole or quadrupole.

23. The illumination method according to claim 14, wherein the linearly
polarized light supplied from the light source has a polarization degree
of 95% or more.

Description:

RELATED APPLICATIONS

[0001] This is a Continuation of application Ser. No. 12/656,822 filed
Feb. 17, 2010, which in turn is a Continuation of application Ser. No.
12/155,301 filed Jun. 2, 2008 (now abandoned), which in turn is a
Continuation of application Ser. No. 11/140,103 filed May 31, 2005 (now
U.S. Pat. No. 7,423,731), which is a Continuation-In-Part of
International Application No. PCT/JP03/015447 filed Dec. 2, 2003. The
disclosure of each prior application is incorporated by reference herein
in its entirety. The disclosure of each of the following priority
applications is herein incorporated by reference in its entirety:
Japanese Patent Application No. 2002-351186 filed Dec. 3, 2002; Japanese
Patent Application No. 2003-201079 filed Jul. 24, 2003; and Japanese
Patent Application No. 2003-338447 filed Sep. 29, 2003.

[0003] In typical exposure apparatus of this type, a secondary light
source, which functions as a substantially planar light source composed
of a plurality of light sources, is formed by a light beam from a light
source that is transmitted through a fly's-eye lens that functions as an
optical integrator. The light beams from the secondary light source are
incident to a condenser lens after being regulated through an aperture
diaphragm positioned near a rear focal plane of the fly's-eye lens.

[0004] The light beams converged by the condenser lens illuminate
superimposingly a mask on which a predetermined pattern is formed. The
light transmitted through mask pattern forms an image on a wafer through
a projection optical system. As a result, the mask pattern is projected
and exposed (transferred) onto the wafer. Because the pattern formed on
the mask is highly integrated, it is necessary to obtain a uniform
illumination distribution on the wafer in order to accurately transfer
the micro patterns onto the wafer.

[0005] Accordingly, attention has been given to a technology in which a
circular secondary light source is formed on the rear focal plane of the
fly's-eye lens, and illumination coherency σ(σ=an aperture
diaphragm diameter/a pupil diameter of a projection optical system; or
σ=an exit-side numerical aperture of an illumination optical
system/an incident-side numerical aperture of the projection optical
system) is changed by varying a size of the secondary light source.
Moreover, attention has been given to a technology in which a depth of
focus and resolution of the projection optical system are improved by
forming an annular or quadrupole secondary light source.

[0006] In the above-described conventional exposure apparatus, normal
circular illumination is performed with a circular secondary light
source, and modified illumination (annular or quadrupole illumination) is
performed with an annular or quadrupole secondary light source, depending
on the characteristics of the mask pattern. However, it is generally the
case that, regardless of the characteristics of the mask pattern, the
mask is illuminated with light whose polarized state is not changed, that
is, light in a nonpolarized state. Appropriate illumination conditions
that are required to precisely transfer the mask pattern onto the wafer
are not always secured.

SUMMARY OF THE INVENTION

[0007] A first object of this invention is to provide an illumination
optical system that, when installed on an exposure apparatus, allows the
achievement of appropriate illumination conditions by changing the
polarized state of the illumination light in accordance with the
characteristics of the mask pattern, while controlling a loss of a light
amount.

[0008] Another object of this invention is to provide an exposure
apparatus and an exposure method that uses an illumination optical system
that changes the polarized state of the illumination light in accordance
with the characteristics of the mask pattern, to perform excellent
exposure under appropriate illumination conditions that are accomplished
in accordance with the characteristics of the mask pattern.

[0009] According to a first aspect, an illumination optical system,
arranged in an optical path between a linearly polarized light source and
an illuminated surface, includes a polarized state switching device that
is positioned in a light path between the light source and the
illuminated surface. The polarized state switching device switches the
polarized state of the light that illuminates the illuminated surface
between a predetermined polarized state and a nonpolarized state. It is
preferable that the polarized state switching device is insertable into
and removable from an illumination light path and includes a depolarizer
that selectively unpolarizes the incident linearly polarized light.

[0010] According to a second aspect, an illumination optical system that
illuminates an illuminated surface under a predetermined polarized state
with light from a light source includes a light directing device that
directs the light from the light source to the illuminated surface and is
positioned in a light path between the light source and the illuminated
surface, and a polarized state fluctuation correcting device that
corrects fluctuations in the polarized state on the illuminated surface
and that is positioned in the light path between the light source and the
illuminated surface.

[0011] According to a third aspect, an illumination optical system that
illuminates an illuminated surface under a predetermined polarized state
with light from a light source includes a light directing device that
directs the light from the light source to the illuminated surface and is
positioned in a light path between the light source and the illuminated
surface, and a polarized state stabilizing device that stabilizes the
polarized state on the illuminated surface and that is positioned in the
light path between the light source and the illuminated surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention will be described in conjunction with the following
drawings of exemplary embodiments in which like reference numerals
designate like elements, and in which:

[0013] FIG. 1 is a diagram schematically showing a structure of an
exposure apparatus equipped with an illumination optical system according
to an exemplary embodiment of this invention;

[0014]FIG. 2A is a diagram showing an annular secondary light source
formed for annular illumination;

[0024] FIG. 11 is a diagram schematically showing an example in which a
quarter-wave plate, which converts elliptically polarized light to
linearly polarized light, is additionally provided for the polarized
state switching device;

[0025] FIG. 12 is a flow chart of a method used for obtaining a liquid
crystal display element as a micro device;

[0026]FIG. 13 is a flow chart of a method for obtaining a semiconductor
element as a micro device;

[0027]FIG. 14 is a diagram schematically explaining an example in which a
mask is illuminated with light in the linearly polarized state under
dipole illumination;

[0028] FIG. 15 is a diagram schematically explaining an example in which a
mask is illuminated with light in the linearly polarized state under
circular illumination;

[0029] FIG. 16 is a diagram schematically showing a structure in which the
exposure apparatus shown in FIG. 1 is additionally provided with a
polarization monitor for detecting the polarized state of the
illumination light;

[0030]FIG. 17 is a perspective view schematically showing an internal
structure of the polarization monitor shown in FIG. 16;

[0031]FIG. 18 is a flow chart of a method for adjusting a crystal optic
axis for the quarter-wave plate and a crystal optic axis for a half-wave
plate in the polarized state switching device shown in FIG. 11;

[0032]FIG. 19 is a diagram showing changes in output of the polarization
monitor at each angular position of the crystal optic axis for the
half-wave plate when the crystal optic axis for the quarter-wave plate is
fixed at a normal angular position of -45 degrees;

[0033]FIG. 20 is a diagram showing changes in output of the polarization
monitor at each angular position of the crystal optic axis for the
half-wave plate when the crystal optic axis for the quarter-wave plate is
set at various angular positions;

[0034] FIG. 21 is a diagram showing changes in output contrast of the
polarization monitor at various angular positions for the crystal optic
axis for the quarter-wave plate;

[0035]FIG. 22 is a diagram showing changes in output of the polarization
monitor at each angular position of the crystal optic axis for the
half-wave plate when the crystal optic axis of the quarter-wave plate is
fixed at the first angular position for converting the elliptically
polarized light to a linearly-polarized light;

[0036]FIG. 23 is a diagram schematically showing a structure of an
exposure apparatus having an illumination pupil distribution forming
device, which has a different structure from the exposure apparatus shown
in FIG. 1 or FIG. 16;

[0037] FIG. 24 is a diagram schematically showing a structure of a conical
axicon system positioned in a light path between a front-side lens group
and a rear-side lens group of an afocal lens shown in FIG. 23;

[0038] FIG. 25 is a diagram explaining functions of the conical axicon
system with respect to the secondary light source formed with an annular
illumination in the exemplary modification shown in FIG. 23;

[0039] FIG. 26 is a diagram explaining functions of a zoom lens with
respect to the second light source formed with the annular illumination
in the exemplary modification shown in FIG. 23;

[0040] FIG. 27 is a diagram schematically showing a structure of the first
cylindrical lens pair and the second cylindrical lens pair, which are
positioned in the light path between the front-side lens group and the
rear-side lens group of the afocal lens shown in FIG. 23;

[0041] FIG. 28 is a diagram explaining the functions of the first
cylindrical lens pair and the second cylindrical lens pair with respect
to the secondary light source formed with the annular illumination of the
exemplary modification shown in FIG. 23;

[0042] FIG. 29 is a diagram explaining the functions of the first
cylindrical lens pair and the second cylindrical lens pair with respect
to the secondary light source formed with the annular illumination in the
exemplary modification shown in FIG. 23; and

[0043] FIG. 30 is a diagram explaining the functions of the first
cylindrical lens pair and the second cylindrical lens pair with respect
to the secondary light source formed with the annular illumination in the
exemplary modification shown in FIG. 23.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0044] According to a first embodiment, an illumination optical system
that has a light source for providing linearly polarized light and that
illuminates an illuminated surface with the light from the light source
includes a polarized state switching device that is positioned in a light
path between the light source and the illuminated surface and that
switches the polarized state of the light that illuminates the
illuminated surface between a predetermined polarized state and a
nonpolarized state.

[0045] The polarized state switching device is insertable into and
removable from an illumination light path and includes a depolarizer that
selectively unpolarizes the incident linearly polarized light.

[0046] According to the first embodiment, the polarized state switching
device varies a polarization plane of the linearly polarized light if the
predetermined polarized state is a linearly polarized state. In addition,
it is preferable that the polarized state switching device includes a
phase member for selectively changing a polarization plane of the
incident linearly polarized light. In this case, the phase member has a
half-wave plate with a crystal optic axis that is rotatable about an
optical axis of the illumination optical system.

[0047] In addition, according to the first embodiment, the depolarizer
includes a crystal prism having a crystal optic axis that is rotatable
about an optical axis of the illumination optical system. In addition, it
is preferable that the depolarizer includes a polarized beam splitter and
a reflection system that returns the light reflected by the polarized
beam splitter back to the polarized beam splitter by reflecting the light
plural times in a plane, such that a light path of light that is
transmitted through the polarized beam splitter and a light path of light
reflected by the polarized beam splitter substantially match each other.
It is preferable that the polarized beam splitter and the reflection
system are integrally rotatable about the optical axis of the
illumination optical system.

[0048] In addition, according to the first embodiment, the depolarizer
includes a polarized beam splitter and a reflection system that returns
the light reflected by the polarized beam splitter back to the polarized
beam splitter by reflecting the light plural times in a plane such that a
light path of light that is transmitted through the polarized beam
splitter and a light path of light reflected by the polarized beam
splitter substantially match each other. It is preferable that the
polarized beam splitter and the reflection system are integrally
insertable into and removable from an illumination light path.

[0049] In addition, according to the first embodiment, the polarized state
switching device further includes a second phase member for converting
incident elliptically polarized light into linearly polarized light. In
this case, it is preferable that the second phase member includes a
quarter-wave plate having a crystal optic axis that is rotatable about an
optical axis of the illumination optical system.

[0050] Further, according to the first embodiment, a light transmissive
member is positioned in the light path between the light source and the
polarized state switching device and is formed by a cubic system
(isometric system) crystal material, and the light transmissive member is
oriented such that a traveling direction of the light becomes closer to a
crystal orientation <111> or <100> than to a crystal
orientation <110>. In this case, it is preferable that the light
transmissive member is positioned in the light path between the polarized
state switching device and the illuminated surface, and is formed by a
cubic system crystal material, and the light transmissive member is
oriented such that a traveling direction of the light becomes closer to a
crystal orientation <111> or <100> than to a crystal
orientation <110>.

[0051] It is preferable that the light transmissive member includes an
optical member fixedly positioned in the light path, and that an optical
axis of the optical member substantially matches the crystal orientation
<111> or <100>. In addition, it is preferable that the light
transmissive member includes a rectangular prism as a rear surface
reflection mirror, that an incident surface and an exit surface of the
rectangular prism substantially match a crystal plane {100}, and that a
reflection surface of the rectangular prism substantially matches a
crystal plane {110}. In addition, it is preferable that the light
transmissive member includes a plane parallel plate for moving light
entering along the optical axis in parallel, and the light transmissive
member is provided in the light path and is inclinable with respect to
the optical axis. It is preferable that the optical axis of the plane
parallel plate substantially matches the crystal orientation <100>.

[0052] In addition, according to the first embodiment, the illumination
optical system also includes an illumination pupil distribution forming
device that forms a predetermined light intensity distribution on or
adjacent to a pupil plane of the illumination optical system, a changing
device that changes at least one of a shape and a size of the
predetermined light intensity distribution, and a light direction optical
system that directs a light beam from the predetermined light intensity
distribution to the illuminated surface. In this case, it is preferable
that the polarized state switching device changes a polarized state of
the light that illuminates the illuminated surface in accordance with the
change in at least one of the shape and the size of the predetermined
light intensity distribution. In addition, it is preferable that the
polarized state switching device switches the polarized state of the
light that illuminates the illuminated surface between a linearly
polarized state and a nonpolarized state in accordance with the change in
at least one of the shape and the size of the predetermined light
intensity distribution.

[0053] In addition, according to the first embodiment, in the
predetermined polarized state, an S1 component of a Stokes parameter of
the light satisfies a condition 0.6 |S1|. In addition, it is preferable
that in the nonpolarized state, S1 and S2 components of a Stokes
parameter of the light satisfy conditions |S1|≦0.1 and
|S2|≦0.1. Moreover, it is preferable that the illumination optical
system further includes a polarized state fluctuation correcting device
that corrects fluctuations of the polarized state on the illuminated
surface, and that the polarized state fluctuation correcting device is
positioned in the light path between the light source and the illuminated
surface. In this case, the polarized state fluctuation correcting device
includes a polarization monitor positioned in the light path between the
polarized state switching device and the illuminated surface to detect
the polarized state of the light, and a controller that controls the
polarized state switching device in response to an output from the
polarization monitor.

[0054] In addition, according to the first embodiment, the polarized state
switching device includes a half-wave plate having a crystal optic axis
that is rotatable about the optical axis of the illumination optical
system, and a quarter-wave plate having a crystal optic axis that is
rotatable about the optical axis of the illumination optical system. In
response to changes in detection results obtained from the polarization
monitor when respectively changing the crystal optic axes of the
quarter-wave plate and the half-wave plate, the controller adjusts an
angular position of the crystal optic axis of the quarter-wave plate to a
predetermined position for converting incident elliptically polarized
light into linearly polarized light, and an angular position of the
crystal optic axis of the half-wave plate to a predetermined position for
converting incident linearly polarized light to linearly polarized light
that has a polarization plane in a predetermined direction. In this case,
it is preferable that the controller adjusts the angular position of the
crystal optic axis of the quarter-wave plate to a first angular position,
at which a contrast for changes in the S1 component of the Stokes
parameter in the detection result becomes substantially maximum, and
changes the angular position of the crystal optic axis of the half-wave
plate to a second angular position at which the S1 component of the
Stokes parameter in the detection result becomes substantially maximum or
substantially minimum while the crystal optic axis of the quarter-wave
plate is set at the first angular position.

[0055] In addition, according to the first embodiment, the polarization
monitor is positioned in the light path between the polarized state
switching device and the illuminated surface and includes a beam splitter
that extracts from the light path reflected light or transmitted light
having a polarized state that is different from the polarized state of
the incident light and a light intensity detector that detects the
intensity of the reflected light or the transmitted light extracted by
the beam splitter. The polarized state of the incident light to the beam
splitter is detected based on an output of the light intensity detector.
In this case, it is preferable that the beam splitter has reflectivity or
transmissivity, in which intensity Ip for p-polarized light and intensity
Is for s-polarized light included in the reflected light or the
transmitted light satisfy a condition that an intensity ratio Ip/Is is
less than 1/2(Ip/Is<1/2) or more than 2 (Ip/Is>2).

[0056] In addition, according to the first embodiment, the illumination
optical system further includes an illumination pupil distribution
forming device that forms a predetermined light intensity distribution on
or adjacent to a pupil plane of the illumination optical system. The
illumination pupil distribution forming device forms two areas having a
high light intensity distribution that are spaced along a direction of
the pupil plane or a surface adjacent thereto that corresponds to a
predetermined first direction on the illuminated surface. The polarized
state switching device sets the polarized state of the light that
illuminates the illuminated surface from the two areas having a high
light intensity distribution to a linearly polarized state that has a
polarization plane in a direction substantially orthogonal to the
predetermined first direction. In this case, the two areas having a high
light intensity distribution are formed symmetrically about the optical
axis of the illumination optical system, and a value σo defined by
a ratio φo/φp satisfies a condition

[0057] 0.7 an where φo is a diameter of a circle about the optical
axis that circumscribes the two areas having a high light intensity
distribution, and φp is a diameter of the pupil plane. It is
preferable that the two areas having a high light intensity distribution
are formed symmetrically about the optical axis of the illumination
optical system, and a value an defined by a ratio φo/φp and
σi defined by a ratio φi/φp satisfy a condition
0.5≦σi/σo where φo is a diameter of a circle about
the optical axis that circumscribes the two areas having a high light
intensity distribution, φp is a diameter of the pupil plane, and
σi is a diameter of a circle about the optical axis that inscribes
the two areas having a high light intensity distribution.

[0058] In a second embodiment, an illumination optical system that
illuminates an illuminated surface under a predetermined polarized state
with light from a light source includes a light directing device that
directs the light from the light source to the illuminated surface and is
positioned in a light path between the light source and the illuminated
surface, and a polarized state fluctuation correcting device that
corrects fluctuations in the polarized state on the illuminated surface
and is positioned in the light path between the light source and the
illuminated surface.

[0059] According to the second embodiment, the polarized state fluctuation
correcting device includes a polarized state adjusting device that
adjusts the polarized state on the illuminated surface and is positioned
in the light path between the light source and the illuminated surface, a
polarization monitor that detects the polarized state of the light and is
positioned in the light path between the light source and the illuminated
surface, and a controller that controls the polarized state adjusting
device in accordance with an output from the polarization monitor. In
this case, it is preferable that the polarized state adjusting device
includes an adjustable phase plate positioned in the light path between
the light source and the polarization monitor. In addition, according to
the second embodiment, it is preferable that the light directing device
includes an optical member having characteristics that change the
polarized state of incident light and then ejects that light. The optical
member may be formed by a crystal optical material.

[0060] In a third embodiment, an illumination optical system that
illuminates an illuminated surface with light from a light source
includes a light directing device that directs the light from the light
source to the illuminated surface and is positioned in a light path
between the light source and the illuminated surface, and a polarized
state stabilizing device that stabilizes the polarized state on the
illuminated surface and is positioned in the light path between the light
source and the illuminated surface.

[0061] According to the third embodiment, the polarized state stabilizing
device includes a polarized state adjusting device that adjusts the
polarized state on the illuminated surface and is positioned in the light
path between the light source and the illuminated surface, a polarization
monitor that detects the polarized state of the light and is positioned
in the light path between the light source and the illuminated surface,
and a controller that controls the polarized state adjusting device in
accordance with an output from the polarization monitor. In this case, it
is preferable that the light directing device includes an optical member
having characteristics that change the polarized state of incident light
and then ejects that light. The optical member may be formed by a crystal
optical material.

[0062] In addition, according to the third embodiment, the polarized state
stabilizing device includes a light transmissive member formed by a cubic
system crystal material that is positioned in the light path between the
light source and the illuminated surface. In this case, it is preferable
that the light transmissive member is oriented such that a traveling
direction of the light becomes closer to a crystal orientation
<111> or <100> than a crystal orientation <110>. In
addition, it is preferable that the light transmissive member includes an
optical member fixedly positioned in the light path and that an optical
axis of the optical member is oriented to substantially match the crystal
orientation <111> or <100>. It may instead be preferable that
the light transmissive member includes a rectangular prism as a rear
surface reflection mirror, that an incident surface and an exit surface
of the rectangular prism are oriented to substantially match a crystal
plane {100}, and that a reflection surface of the rectangular prism is
oriented to substantially match a crystal plane {110}. It may instead be
preferable that the light transmissive member includes a plane parallel
plate for moving light entering along the optical axis in parallel and
that is provided in the light path and is inclinable with respect to the
optical axis, and that the optical axis of the plane parallel plate is
oriented to substantially match the crystal orientation <100>.

[0063] According to a fourth embodiment, a method for adjusting an
illumination optical system that illuminates an illuminated surface in a
predetermined polarized state by light from a light source includes a
wavelength plate setting step that sets a quarter-wave plate in an
illumination light path of the illumination optical system such that a
crystal optic axis of the quarter-wave plate is set at a predetermined
angular position, and sets a half-wave plate in the illumination light
path such that a crystal optic axis of the half-wave plate is set at a
predetermined angular positioned. Based on a result of detection of the
polarized state of the light in the light path between a polarized state
switching device and the illuminated surface, the crystal optic axes of
the quarter-wave plate and the half-wave plate are respectively changed.
The wavelength plate setting step sets the crystal optic axis of the
quarter-wave plate at a desired position for converting incident
elliptically polarized light into linearly polarized light and the
crystal optic axis of the half-wave plate at a standard position for
converting incident linearly polarized light into linearly polarized
light that has a polarization plane in a predetermined direction.

[0064] According to the fourth embodiment, the crystal optic axis of the
quarter-wave plate is set at a first angular position, at which a
contrast for changes in an S1 component of a Stokes parameter becomes
substantially maximum in the detection result, and the crystal optic axis
of the half-wave plate is set at a second angular position at which the
S1 component of the Stokes parameter becomes substantially maximum or
substantially minimum in the detection result while the crystal optic
axis of the quarter-wave plate is set at the first angular position. In
addition, it is preferable that the method also includes an illumination
pupil forming step that forms a predetermined light intensity
distribution on or adjacent to a pupil plane of the illumination optical
system by the light from the light source, an illumination pupil changing
step that changes at least one of a shape and a size of the predetermined
light intensity distribution, and a wavelength plate resetting step that
resets at least one of the crystal optic axes of the quarter-wave plate
and the half-wave plate.

[0065] According to a fifth embodiment, an exposure apparatus that
includes the illumination optical system described in the first-third
embodiments or the illumination optical system adjusted by the adjustment
method described in the fourth embodiment is provided.

[0066] According to the fifth embodiment, the exposure apparatus also
includes a projection optical system that is positioned in the light path
between a first plane at which the mask is positioned, and a second plane
at which the photosensitive substrate is positioned, and that forms an
image of a pattern of the mask onto the second plane, a pupil intensity
distribution forming device that forms a predetermined light intensity
distribution at a position conjugate to the pupil of the projection
optical system or a position adjacent thereto, and a pupil intensity
distribution changing device that changes at least one of a shape and a
size of the predetermined light intensity distribution. In this case, it
is preferable that the exposure apparatus also includes a polarized state
changing device that is positioned in the light path between the light
source and the illuminated surface and changes the polarized state of the
light that illuminates the illuminated surface. The pupil intensity
distribution changing device preferably changes at least one of the shape
and the size of the predetermined light intensity distribution in
accordance with pattern characteristics of the mask. The polarized state
changing device preferably changes the polarized state of the light that
illuminates the illuminated surface in accordance with at least one of
the shape and the size of the predetermined light intensity distribution.
In addition, it is preferable that the polarized state changing device
includes a polarized state switching device that switches the polarized
state of the light that illuminates the illuminated surface between a
predetermined polarized state and a nonpolarized state, and that the
polarized state switching device switches between the predetermined
polarized state and the nonpolarized state in accordance with a change in
at least one of the shape and the size of the predetermined light
intensity distribution.

[0067] Furthermore, according to the fifth embodiment, the pupil intensity
distribution forming device forms two areas having a high light intensity
distribution that are spaced away from each other along a pitch direction
of a line-and-space pattern formed on the mask. The polarized state
changing device sets the polarized state of the light that illuminates
the illuminated surface from the two areas having a high light intensity
distribution to a linearly polarized state that has a polarization plane
in a direction orthogonal to the pitch direction. Instead, it may be
preferable that the pupil intensity distribution forming device forms one
area having a high light intensity distribution substantially about the
optical axis of the illumination optical system, and that the polarized
state changing device sets the polarized state of the light that
illuminates the illuminated surface from the one area having a high light
intensity distribution to the linearly polarized state that has a
polarization plane in a direction substantially orthogonal to the pitch
direction of the line-and-space pattern formed on a phase shift mask as
the mask. In this case, it is preferable that the value σ that is
defined by a ratio φ/φp satisfies a condition σ≦0.4
where φ is a size of the one area having a high light intensity
distribution, and φp is a diameter of the pupil plane.

[0068] In a sixth embodiment, an exposure method includes an illumination
step that illuminates a mask through the illumination optical system of
the first-third embodiments or an illumination optical system adjusted in
accordance with the adjustment method of the fourth embodiment, and an
exposure step that exposes a pattern on the mask onto the photosensitive
substrate positioned on the illuminated surface.

[0069] According to the sixth embodiment, the exposure method further
includes a projection step that forms an image of the pattern on the mask
using a projection optical system, a pupil intensity distribution forming
step that forms a predetermined light intensity distribution at a
position conjugate to the pupil of the projection optical system or a
position adjacent thereto, and a pupil intensity distribution changing
step that changes at least one of a shape or a size of the predetermined
light intensity distribution. In this case, it is preferable that the
pupil intensity distribution changing step changes at least one of the
shape and the size of the predetermined light intensity distribution in
accordance with pattern characteristics of the mask, and that the
exposure method also includes a polarized state changing step that
changes a polarized state of the light that illuminates the illuminated
surface in accordance with a change in the at least one of the shape and
the size of the predetermined light intensity distribution.

[0070] In addition, according to the sixth embodiment, the pupil intensity
distribution forming step forms two areas having a high light intensity
distribution spaced away from each other along a pitch direction of a
line-and-space pattern formed on the mask, and the exposure method also
includes a step that sets the polarized state of the light that
illuminates the illuminated surface from the two areas having a high
light intensity distribution to a linearly polarized state that has a
polarization plane in a direction substantially orthogonal to the pitch
direction. In this case, it is preferable that the two areas having a
high light intensity distribution are formed symmetrically about the
optical axis of the illumination optical system, and that a value
σo defined by a ratio φo/φp satisfies a condition
0.7≦σo where φo is a diameter of a circle about the
optical axis that circumscribes the two areas having a high light
intensity distribution, and φp is a diameter of the pupil plane. In
addition, it is preferable that the two areas having a high light
intensity distribution are formed symmetrically about the optical axis of
the illumination optical system, and that a value σo defined by a
ratio φo/φp and σi defined by a ratio φi/φp satisfy
a condition 0.5≦σi/σo where φo is a diameter of a
circle about the optical axis that circumscribes the two areas having a
high light intensity distribution, φp is a diameter of the pupil
plane, and σi is a diameter of a circle about the optical axis that
inscribes the two areas having a high light intensity distribution.

[0071] In a seventh embodiment, an exposure method for exposing a pattern
on a mask positioned at a first plane onto a photosensitive substrate
positioned at a second plane includes a first step that provides linearly
polarized light, a second step that illuminates the mask with the light
provided in the first step, a third step that exposes the pattern on the
mask illuminated in the second step onto the photosensitive substrate,
and a fourth step that switches a polarized state of the light on the
second plane between a predetermined polarized state and a nonpolarized
state while controlling a loss of a light amount.

[0072] According to the seventh embodiment, the fourth step includes a
step that varies a polarization plane for linearly polarized light. In
addition, it is preferable that the third step includes a step that forms
an image of the pattern on the mask onto the second plane using a
projection optical system, and that the exposure method also includes a
fifth step that forms a predetermined light intensity distribution at a
position conjugate to a pupil of the projection optical system or a
position adjacent thereto, a sixth step that changes at least one of a
shape or a size of the predetermined light intensity distribution, and a
seventh step that changes a polarized state of the light that illuminates
the illuminated surface in accordance with the change in at least one of
the shape and the size of the predetermined light intensity distribution.

[0073] In an eighth embodiment, an exposure method for exposing a pattern
on a mask positioned at a first plane onto a photosensitive substrate
positioned at a second plane includes a first step that provides light, a
second step that illuminates the mask with light provided in the first
step, a third step that exposes the pattern on the mask illuminated in
the second step onto the photosensitive substrate, and a fourth step that
corrects fluctuations of a polarized state of the light on the second
plane.

[0074] According to the eighth embodiment, the exposure method also
includes a fifth step that detects the polarized state of the light, and
the fourth step includes a step that adjust the polarized state on the
second plane based on the polarized state of the light detected in the
fifth step,

[0075] In a ninth embodiment, an illumination optical system that
illuminates an illuminated surface under a predetermined polarized state
with light from a light source includes a polarized state changing device
that is positioned in a light path between the light source and the
illuminated surface and changes the polarized state of the light that
illuminates the illuminated surface, and a vertical/horizontal ratio
changing device that changes a vertical/horizontal ratio of a light
intensity distribution formed on an illumination pupil that is
substantially in a Fourier transform plane relationship with the
illuminated pupil.

[0076] According to the ninth embodiment, the polarized state changing
device includes a polarized state switching device that changes the
polarized state of the light that illuminates the illuminated surface
between the predetermined polarized state and a nonpolarized state. In
addition, according to the ninth embodiment, the vertical/horizontal
ratio changing device includes an optical element that is positioned at
or adjacent to a position that is substantially in the Fourier transform
plane relationship with the illumination pupil and has a function to
change a power ratio in two orthogonal directions.

[0077] In a tenth embodiment, an exposure apparatus is provided that
includes the illumination optical system of the ninth embodiment and
exposes a pattern on a mask onto a photosensitive substrate positioned on
the illuminated surface.

[0078] According to the tenth embodiment, the polarized state changing
device changes the polarized state of the light in accordance with the
pattern characteristics of the mask, and the vertical/horizontal ratio
changing device changes the vertical/horizontal ratio of the light
intensity distribution formed on the illumination pupil in accordance
with the pattern characteristics of the mask.

[0079] In an eleventh embodiment, an exposure method for exposing a
pattern on a mask positioned at a first plane onto a photosensitive
substrate positioned at a second plane includes a first step that
provides light having a predetermined polarization, a second step that
illuminates the mask with the light provided in the first step, a third
step that exposes the pattern on the mask illuminated in the second step
onto the photosensitive substrate, a fourth step that changes a polarized
state of the light on the second plane, and a fifth step that changes a
vertical/horizontal ratio of a light intensity distribution formed on an
illumination pupil that is substantially in a Fourier transform plane
relationship with the second plane.

[0080] According to the eleventh embodiment, the fourth step changes the
polarized state of the light in accordance with the pattern
characteristics of the mask. In addition, according to the eleventh
embodiment, the fifth step changes the vertical/horizontal ratio of the
light intensity distribution formed on the pupil plane in accordance with
the pattern characteristics of the mask.

[0081] In a twelfth embodiment, an illumination optical system that
illuminates an illuminated surface with light from a light source
includes a polarized state illumination setting device that sets a
polarized state of the light that illuminates the illuminated surface to
a predetermined polarized state, and an optical integrator positioned in
a light path between the light source and the illuminated surface. The
optical integrator includes a first one-dimensional cylindrical lens
array arranged with a pitch along a predetermined first direction and a
second one-dimensional cylindrical lens array arranged with a pitch along
a second direction that crosses the first direction.

[0082] According to the twelfth embodiment, the first and second
one-dimensional cylindrical lens arrays are integrally provided with a
single light transmissive substrate. In addition, according to the
twelfth embodiment, the illumination optical system also includes a
plurality of cylindrical lens array plates having the first and second
one-dimensional cylindrical lens arrays, and the plurality of cylindrical
lens array plates are positioned with a space from each other along a
direction of an optical axis of the illumination optical system.
Furthermore, at least one of the pitch along the first direction of the
first one-dimensional cylindrical lens array and the pitch along the
second direction of the second one-dimensional cylindrical lens array is
equal to or less than 2 mm.

[0083] In a thirteenth embodiment, an exposure apparatus includes the
illumination optical system of the twelfth preferred embodiment and
exposes a pattern on a mask onto a photosensitive substrate positioned on
the illuminated surface.

[0084] In a fourteenth embodiment, an exposure method includes an
illumination step that illuminates a mask using the illumination optical
system of the twelfth embodiment, and an exposure step that exposes a
pattern on the mask onto a photosensitive substrate positioned on the
illuminated surface.

[0085] Exemplary embodiments of this invention are explained with
reference to the attached drawings.

[0086] FIG. 1 is a diagram schematically showing a structure of an
exposure apparatus equipped with an illumination optical system according
to an exemplary embodiment of this invention. In FIG. 1, the Z axis is
set in a normal direction of a wafer W, which is a photosensitive
substrate. The Y axis is set in a direction on the wafer surface parallel
with the plane of FIG. 1. The X axis is set in a direction in the wafer
surface perpendicular to the plane of the FIG. 1. In addition, in FIG. 1,
the illumination optical system is configured to perform annular
illumination.

[0087] The exposure apparatus of this embodiment is equipped with a laser
light source 1 for providing exposure light (illumination light). A KrF
excimer laser light source, which provides light with a wavelength of 248
nm, or an ArF excimer laser light source, which provides light with a
wavelength of 193 nm, for example, may be used as the laser light source
1. A light beam with substantially parallel light rays illuminated from
the laser light source I along the Z direction has a rectangular cross
section that is elongated in the X direction and enters into a beam
expander 2 formed of a pair of lenses 2a and 2b. The lenses 2a and 2b
have negative refractive power and positive refractive power,
respectively, in the plane of FIG. 1 (in the YZ plane). Therefore, the
light beam that enters into the beam expander 2 is expanded in the plane
of FIG. 1 and shaped into a light beam that has a predetermined
rectangular cross section.

[0088] The light beam with substantially parallel light rays transmitted
through the beam expander 2, which functions as a shaping optical system,
enters to an afocal zoom lens 5 through a phase member 10, a depolarizer
(depolarization element) 20, and a diffractive optical element , after
being deflected in the Y direction by a folding mirror 3. Structures and
functions of the phase member 10 and the depolarizer 20 will be described
later. In general, the diffractive optical element is formed by forming
steps on a substrate such that the steps have a pitch of approximately
the wavelength of the exposure light (illumination light), and have a
function to diffract the incident light beam in a predetermined angle. In
detail, the diffractive optical element has a function to form a circular
light intensity distribution in a far field (or Fraunhofer diffraction
region) when a light beam with parallel light rays having a circular
cross section enters the diffractive optical element 4.

[0089] Therefore, the light beam transmitted through the diffractive
optical element forms a circular light intensity distribution, that is,
a light beam having a circular cross section, at a pupil position of the
afocal zoom lens 5. The diffractive optical element is structured to be
removable from the path of the illumination light. The afocal zoom lens 5
is structured such that a magnification can be changed continuously in a
predetermined range while maintaining an afocal system (afocal optical
system). The light beam transmitted through the afocal zoom lens 5 enters
a diffractive optical element 6 for annular illumination. The afocal zoom
lens 5 connects, with substantially optical conjugation the origin of
divergence by the diffractive optical element and a diffractive surface
of the diffractive optical element 6. The numerical aperture of the light
beam converged to a point on the diffractive surface or a plane adjacent
thereto of the diffractive optical element 6 varies depending on the
magnification of the afocal zoom lens 5.

[0090] The diffractive optical element 6 for annular illumination
functions to form a ring-shaped light intensity distribution in a far
field thereof when a light beam having parallel rays is incident thereto.
The diffractive optical element 6 is structured so as to be insertable
into the path of the illumination light, and replaceable with a
diffractive optical element 60 for quadrupole illumination, a diffractive
optical element 61 for circular illumination, a diffractive optical
element 62 for dipole illumination along the X axis, or a diffractive
optical element 63 for dipole illumination along the Y axis. Structures
and functions of the diffractive optical element 60 for quadrupole
illumination, the diffractive optical element 61 for circular
illumination, the diffractive optical element 62 for dipole illumination
along the X axis, or the diffractive optical element 63 for dipole
illumination along the Y axis will be described later.

[0091] The light beam transmitted through the diffractive optical element
6 enters into a zoom lens 7. Near the rear focal plane of the zoom lens
7, an incident surface of a micro lens array (or a fly's-eye lens) 8 is
positioned. The micro lens array 8 is an optical element formed of many
micro lenses having a positive refractive power arranged densely in a
matrix form. In general, a micro lens array is structured by forming a
micro lens group by, for example, etching a plane parallel plate.

[0092] Each of the micro lenses forming the micro lens array is smaller
than each of the lens elements structuring a fly's-eye lens. Moreover, in
the micro lens array, many micro lenses (micro refractive surfaces) are
integrally formed without being mutually isolated from each other, which
is different from the fly's-eye lens, in which lens elements are mutually
isolated from each other. However, the micro lens array is a wavefront
splitting type optical integrator, which is the same as the fly's-eye
lens, in that lens elements having positive refractive power are arranged
in a matrix form.

[0093] As described above, the light beam from the circular light
intensity distribution formed at the pupil position of the afocal zoom
lens 5 through the diffractive optical element enters the diffractive
optical element 6 as a light beam having various angular components,
after exiting from the afocal zoom lens 5. That is, the diffractive
optical element forms an optical integrator that functions to form an
angular light beam (a non-parallel light beam having an angular
distribution). On the other hand, the diffractive optical element 6 has a
function as a light beam conversion element that forms a ring-shaped
light intensity distribution at a far field thereof, when the light beam
with parallel light rays enters the diffractive optical element 6.
Therefore, the light beam transmitted through the diffractive optical
element 6 forms an annular illumination field about an optical axis AX,
for example, in the rear-side focal plane of zoom lens 7 (therefore, an
incident surface of the micro lens array 8).

[0094] An outer diameter of the annular illumination field formed on the
incident surface of the micro lens array 8 varies depending on a focal
length of the zoom lens 7. As such, the zoom lens 7 brings the
diffractive optical element 6 and the incident surface of the micro lens
array 8 into a substantial Fourier transform relationship. The light beam
that entered the micro lens array 8 is divided two-dimensionally. Many
light sources (hereinafter referred to as "secondary light source") in an
annular shape, which is the same as the illumination field formed by the
incident light beam, are formed on the rear focal plane of the micro lens
array 8 as shown in FIG. 2A.

[0095] The light beam from the annular secondary light sources formed in
the rear focal plane of the micro lens array 8 superimposingly
illuminates a mask M, on which a predetermined pattern is formed, after
being converged by a condenser optical system 9. The light beam
transmitted through the pattern on the mask M forms an image of the
pattern of the mask onto a wafer, which is a photosensitive substrate,
through a projection optical system PL. Accordingly, by performing batch
or scan exposure while two-dimensionally driving and controlling the
wafer Win a plane perpendicular to the optical axis AX of the projection
optical system PL (XY plane), the pattern on the mask M is successively
exposed in each exposure region of the wafer W.

[0096] In this embodiment, even if the magnification of the afocal zoom
lens 5 is changed, the center height (a distance to a center line of the
circular shape from the optical axis AX) d0 of the annular secondary
light source does not change, but only the width (1/2 of a difference
between the outer radius (diameter) and the inner radius (diameter)) w0
of the annular secondary light source changes. That is, by changing the
magnification of the afocal zoom lens 5, both the size (outer diameter)
and the shape (annular ratio: inner diameter/outer diameter) of the
annular secondary light source may be changed.

[0097] Furthermore, if the focal length of the zoom lens 7 is changed, the
center height d0 and the width w0 of the annular secondary light source
are both changed without the annular ratio being changed. That is, by
changing the focal length of the zoom lens 7, the outer diameter of the
annular secondary light source may be changed without the annular ratio
thereof being changed. Accordingly, in this embodiment, by appropriately
changing the magnification of the afocal zoom lens 5 and the focal length
of the zoom lens 7, only the annular ratio of the annular secondary light
source may be changed without changing the outer diameter thereof.

[0098] Moreover, quadrupole illumination can be achieved by setting the
diffractive optical element 60, instead of the diffractive optical
element 6, in the illumination light path. The diffractive optical
element 60 for quadrupole illumination has a function to form a quadruple
light intensity distribution in the far field thereof, when the light
beam with parallel light rays enters it. Therefore, the light beam
transmitted through the diffractive optical element 60 forms on the
incident surface of the micro lens array 8 a quadrupole illumination
field comprised of four disc-shaped illumination fields around the
optical axis, for example. As a result, as shown in FIG. 2B, a quadrupole
secondary light source, which is the same as the illumination field
formed on the incident surface of the micro lens array 8, also is formed
in the rear focal plane of the micro lens array 8.

[0099] Similar to the case of annular illumination, in quadrupole
illumination, by changing the magnification of the afocal zoom lens 5,
both the outer diameter (diameter of a circle circumscribing the four
disc-shaped planar light sources) Do and the annular ratio (a diameter Di
of a circle inscribing the four disc-shaped planar light sources/a
diameter Do of the circle circumscribing the four disc-shaped planar
light sources) of the quadrupole secondary light sources can be changed.
In addition, by changing the focal length of the zoom lens 7, the outer
diameter of the quadrupole light source can be changed without changing
the annular ratio thereof. As a result, by appropriately changing the
magnification of the afocal zoom lens 5 and the focal length of the zoom
lens 7, only the annular ratio of the quadrupole secondary light source
may be changed without changing the outer diameter thereof.

[0100] Moreover, by removing the diffractive optical element from the
illumination light path and setting the diffractive optical element 61
for circular illumination, instead of the diffractive optical element 6
or 60, in the illumination light path, normal circular illumination may
be achieved. In this case, the light beam having a rectangular cross
section enters the afocal zoom lens 5 along the optical axis AX. The
light beam that enters the afocal zoom lens 5 is expanded or reduced in
accordance with the magnification thereof. The light beam then exits from
the afocal zoom lens 5 along the optical axis AX while maintaining the
rectangular cross section, and enters the diffractive optical element 61.

[0101] The diffractive optical element 61 for circular illumination has,
similar to the diffractive optical element , a function to form a
circular light intensity distribution in the far field thereof, when the
light beam with parallel light rays having the rectangular cross section
enters it. Therefore, the circular light beam formed by the diffractive
optical element 61 forms a circular illumination field about the optical
axis AX in the incident surface of the micro lens array 8. As a result, a
circular secondary light source centered about the optical axis AX also
is formed in the rear focal plane of the micro lens array 8. In this
case, by changing the magnification of the afocal zoom lens 5 and the
focal length of the zoom lens 7, the outer diameter of the circular
secondary light source can be appropriately changed.

[0102] Moreover, dipole illumination in the X direction may be achieved by
setting the diffractive optical element 62 in the illumination light
path, instead of the diffractive optical elements 6, 60 or 61. The
diffractive optical element 62 for dipole illumination in the X direction
functions to form a dipole light intensity distribution with illumination
fields spaced apart along the X direction in the far field thereof when
the light beam with parallel light rays enters it. Therefore, the light
beam transmitted through the diffractive optical element 62 forms on the
incident surface of the micro lens array 8 a dipole illumination field
formed of two circular illumination fields about the optical axis AX,
which are spaced apart along the X direction, for example. As such, as
shown in FIG. 3A, the dipole secondary light source formed along the X
direction, which is the same as the illumination fields formed on the
incident surface of the micro lens array 8, also is formed on the
rear-side focal plane of the micro lens array 8.

[0103] Furthermore, dipole illumination in the Y direction may be achieved
by setting the diffractive optical element 63 in the illumination light
path, instead of the diffractive optical element 6, 60, 61 or 62. The
diffractive optical element 63 for the dipole illumination in the Y
direction functions to form a dipole light intensity distribution with
illuminated fields spaced apart in the Z direction (corresponding to the
Y direction on the mask and the wafer), in the far field thereof when the
light beam with parallel light rays enters it. Therefore, the light beam
transmitted through the diffractive optical element 63 forms on the
incident surface of the micro lens array 8 a dipole illumination field
formed of the two circular illumination fields spaced apart along the Z
direction, about the optical axis AX, for example. As such, as shown in
FIG. 3B, the dipole secondary light source formed along the Z direction,
which is the same as the illumination fields formed on the incident
surface of the micro lens array 8, also is formed on the rear-side focal
plane of the micro lens array 8.

[0104] Similar to the case of the quadrupole illumination, in the dipole
illumination, by changing the magnification of the afocal zoom lens 5,
both the outer diameter (diameter of a circle circumscribing the two
disc-shaped planar light sources) Do and the annular ratio (a diameter Di
of a circle inscribing the two disc-shaped planar light sources/a
diameter Do of the circle circumscribing the two disc-shaped planar light
sources) of the dipole secondary light sources may be changed. In
addition, by changing the focal length of the zoom lens 7, the outer
diameter of the dipole light source may be changed without the annular
ratio thereof being changed. As a result, by appropriately changing the
magnification of the afocal zoom lens 5 and the focal length of the zoom
lens 7, only the annular ratio of the dipole secondary light source may
be changed without changing the outer diameter thereof.

[0105] FIG. 4 is a diagram schematically showing a structure of the phase
member and the depolarizer shown in FIG. 1. Referring to FIG. 1, the
phase member 10 is formed from a half-wave plate, structured so that its
crystal optic axis is rotatable about the optical axis AX. The
depolarizer is formed from a wedge crystal prism 20a and a wedge silica
prism 20b, which has a complimentary shape to the crystal prism 20a. As
an integral prism assembly, the crystal prism 20a and the silica prism
20b are structured to be removable from the illumination light path. When
using a KrF excimer laser light source or an ArF excimer laser light
source as the laser light source 1, substantially linearly polarized
light enters into the half-wave plate 10 because the light ejected from
these light sources typically has a degree of polarization of 95% or
more.

[0106] If the crystal optic axis of the half-wave plate 10 is configured
to form an angle of 0 or 90 degrees with respect to a polarization plane
of the incident linearly polarized light, the linearly polarized light
that enters the half-wave plate is transmitted through the half-wave
plate 10 as is, without changing its polarization plane. If the crystal
optic axis of the half-wave plate 10 is configured to form an angle of 45
degrees with respect to a polarization plane of the incident linearly
polarized light, the linearly polarized light that enters the half-wave
plate 10 is converted to linearly polarized light in which the
polarization plane is changed by 90 degrees. Furthermore, if the crystal
optic axis of the crystal prism 20a is configured to form an angle of 45
degrees with respect to a polarization plane of the incident linearly
polarized light, the linearly polarized light that enters the crystal
prism 20a is converted into light having a nonpolarized state
(nonpolarized light).

[0107] In this embodiment, the crystal optic axis of the crystal prism 20a
is configured to form an angle of 45 degrees with respect to a
polarization plane of the incident linearly polarized light when the
depolarizer 20 is positioned in the illumination light path. If the
crystal optic axis of the crystal prism 20a is configured to form an
angle of 0 or 90 degrees with respect to a polarization plane of the
incident linearly polarized light, the linearly polarized light that
enters the crystal prism 20a is transmitted through the crystal prism 20a
as is, without changing its polarization plane. Moreover, if the crystal
optic axis of the half-wave plate 10 is configured to form an angle of
22.5 degrees with respect to a polarization plane of the incident
linearly polarized light, the linearly polarized light that enters the
half-wave plate 10 is converted to light having a nonpolarized state that
includes a linearly polarized component, by which the light is
transmitted through the half-wave plate 10 without changing its
polarization plane, and a linearly polarized component by which the
polarization plane is change by 90 degrees.

[0108] As described above, in this embodiment, the linearly polarized
light from the laser light source 1 enters the half-wave plate 10. To
simplify explanations described below, it is assumed that P-polarized
light (linearly polarized light having a polarization plane in the Z
direction at the position of the half-wave plate in FIG. 1; hereinafter
referred to as "polarized in Z direction") enters the half-wave plate 10.
When the depolarizer 20 is positioned in the illumination light path, if
the crystal optic axis of the half-wave plate 10 is configured to form an
angle of 0 or 90 degrees with respect to a polarization plane of the
incident P-polarized light (polarized in the Z direction), the
P-polarized light that enters the half-wave plate 10 is transmitted
through the half-wave plate 10 as is and enters the crystal prism 20a
without changing its polarization plane. Because the crystal optic axis
of the crystal prism 20a is configured to form an angle of 45 degrees
with respect to a polarization plane of the incident P-polarized light
(polarized in the Z direction), the P-polarized light (light polarized in
the Z direction) that enters the crystal prism 20a is converted into
light having a nonpolarized state (a depolarized state).

[0109] The nonpolarized light transmitted through the crystal prism 20a
illuminates the mask M (and therefore the wafer W) in the nonpolarized
state through the silica prism 20b, which functions as a compensator to
compensate in the traveling direction of the light. On the other hand, if
the crystal optic axis of the half-wave plate 10 is configured to form an
angle of 45 degrees with respect to a polarization plane of the incident
P-polarized light, the polarization plane for the P-polarized light
(polarized in the Z direction) that enters the half-wave plate 10 is
changed by 90 degrees and enters the crystal prism 20a as S-polarized
light (linearly polarized light having a polarization plane in the X
direction at the position of the half-wave plate in FIG. 1; hereinafter
referred to as "polarized in the X direction"). Because the crystal optic
axis of the crystal prism 20a is also configured to form an angle of 45
degrees with respect to a polarization plane of the incident S-polarized
light (polarized in the X direction), the S-polarized (polarized in the X
direction) light that enters the crystal prism 20a is converted into
nonpolarized light and illuminates the mask M in the nonpolarized state
through the silica prism 20b.

[0110] On the other hand, when the depolarizer 20 is removed from the
illumination light path, if the crystal optic axis of the half-wave plate
is configured to form an angle of 0 or 90 degrees with respect to a
polarization plane of the incident P-polarized light (polarized in the Z
direction), the P-polarized (polarized in the Z direction) light that
enters the half-wave plate 10 is transmitted through the half-wave plate
10 as is as P-polarized light (polarized in the Z direction) without its
polarization plane being changed. Therefore, the mask M is illuminated by
the P-polarized light (polarized in the Z direction). If the crystal
optic axis of the half-wave plate 10 is configured to faun an angle of 45
degrees with respect to a polarization plane of the incident P-polarized
light (polarized in the Z direction), the P-polarized light that enters
the half-wave plate 10 becomes S-polarized light as its polarization
plane is changed by 90 degrees, and the mask M is illuminated with the
S-polarized light (polarized in the X direction).

[0111] As described above, according to this invention, the mask M can be
illuminated in a nonpolarized state by positioning the depolarizer 20 in
the illumination light path. The mask M may be illuminated in a
P-polarized state (polarized in the Y direction) by removing the
depolarizer 20 from the illumination light path and setting the crystal
optic axis of the half-wave plate 10 to form an angle of 0 or 90 degrees
with respect to a polarization plane of the incident P-polarized light
(polarized in the Z direction). The mask M may be illuminated in the
S-polarized state (polarized in the X direction) by removing the
depolarizer 20 from the illumination light path and setting the crystal
optic axis of the half-wave plate 10 to form an angle of 45 degrees with
respect to a polarization plane of the incident P-polarized light
(polarized in the Z direction).

[0112] In other words, in this embodiment, with the operations of the
polarized state switching device that is composed of the half-wave plate
10 and the depolarizer 20, the polarized state for the light that
illuminates the mask (and therefore the wafer W), which has a surface to
be illuminated, may be switched between the linearly polarized state and
the nonpolarized state. In addition, the polarized state may be switched
between the P-polarized state and the S-polarized state (between the
polarized states that are perpendicular to each other) (polarization
planes for the linearly polarized light may be varied) when illuminating
the mask M with the linearly polarized light. As a result, in this
embodiment, appropriate illumination conditions can be achieved by
changing the polarized state for the illumination light while controlling
the loss of light amount in accordance with the characteristics of the
patterns on the mask M. Therefore, the wafer W can be exposed well under
an appropriate illumination condition achieved in accordance with the
characteristics of the pattern on the mask M. In particular, when
illuminating the mask M with the linearly polarized light, the linearly
polarized light from the light source 1 may be directed to the
illuminated surface using the polarized state switching device without
substantially losing the light amount.

[0113] In detail, by setting to the dipole illumination in the X
direction, for example, and by illuminating the mask with the light in
the linearly polarized state having the polarization plane along the X
direction on the mask M, a pattern having extremely narrow line widths in
the X direction may be accurately exposed onto a critical layer on the
wafer W. Subsequently, by switching to the dipole illumination in the X
direction, for example, and by illuminating the mask M with the linearly
polarized light that has the polarization plane along the Y direction on
the mask M, a pattern having extremely narrow line widths in the Y
direction may be accurately exposed onto the critical layer on the wafer
W.

[0114] Furthermore, after completing the double exposure on the critical
layer, a two-dimensional pattern that has relatively wide line widths may
be exposed on the non-critical layer (middle layer or rough layer) on the
wafer W at a high throughput by, for example, maintaining the dipole
illumination, or by switching to the quadrupole, annular, or circular
illumination and illuminating the mask with light in the nonpolarized
state. However, these are only examples. In general, the wafer W may be
exposed well under appropriate illumination conditions by setting the
secondary light source at an appropriate shape and size and setting the
light that illuminates the mask M in an appropriate polarized state in
accordance with the characteristics of the pattern on the mask M.

[0115] For practical purposes, scattering of light on a resist layer
formed on the wafer W differs when the P-polarized light beam is
diagonally incident on the wafer W and when the S-polarized light beam is
diagonally incident on the wafer W. In detail, the S-polarized light has
higher reflectivity than the P-polarized light so that the P-polarized
light beam reaches deeper inside the resist layer than the S-polarized
light beam. By using such a difference in the optical characteristics of
the P-polarized light and the S-polarized light with respect to the
resist layer, and by achieving appropriate illumination conditions by
changing the polarized state for the illumination light in accordance
with the characteristics of the pattern on the mask M, the wafer W may be
exposed well under appropriate illumination conditions.

[0116] In the above-described embodiment, the half-wave plate 10, which is
a phase member for changing the polarization plane of the incident
linearly polarized light as needed, is positioned on the light source
side, and the depolarizer 20, which unpolarizes the incident linearly
polarized light as need, is positioned on the mask side. However, they
are not limited to this arrangement, and the same optical functions and
effects may be obtained even if the depolarizer 20 is positioned on the
light source side, and the half-wave plate 10 is positioned on the mask
side.

[0117] Moreover, in the above-described embodiment, the silica prism 20b
is used as a compensator to compensate the traveling direction of the
light transmitted through the crystal prism 20a. However, the invention
is not limited to this, and a wedge-shaped prism may be formed by an
optical material, such as quartz or fluorite, which has high durability
with respect to the KrF excimer laser beam or the ArF excimer laser beam.
This applies similarly in other related exemplary modifications.

[0118] FIG. 5 is a diagram schematically showing a structure of a
polarized state switching device according to a first exemplary
modification. The polarized state switching device according to the first
modification shown in FIG. 5 has a structure similar to that of the
polarized state switching device according to the embodiment shown in
FIG. 4. However, in contrast with the embodiment in FIG. , in which the
depolarizer 20 is structured to be removable from the illumination light
path, the first exemplary modification in FIG. 5 is basically different
in that the crystal prism 20a and the silica prism 20b, which together
form the depolarizer 20, are structured to be integrally rotatable about
the optical axis AX, and that the crystal optic axis of the crystal prism
20a is structured to be rotatable about the optical axis AX. The first
exemplary modification shown in FIG. 5 is explained below, focusing on
the differences from the embodiment shown in FIG. 4.

[0119] In the first exemplary modification, if the crystal optic axis of
the half-wave plate 10 is set to form an angle of 45 degrees with respect
to a polarization plane of the incident P-polarized light (polarized in
the Z direction), the P-polarized light (polarized in the Z direction)
that enters the half-wave plate 10 is transmitted through the half-wave
plate 10 and enters the crystal prism 20a as is in P-polarization
(polarized in the Z direction) without changing the polarization plane of
the light. At this time, if the crystal optic axis of the crystal prism
20a is set to form an angle of 45 degrees with respect to a polarization
plane of the incident P-polarized light (polarized in the Z direction),
the P-polarized light (polarized in the Z direction) that enters the
crystal prism 20a is converted into light in the nonpolarized state, and
the mask M is illuminated by the light in the nonpolarized state that is
transmitted through the quartz prism 20a. Moreover, if the crystal optic
axis of the crystal prism 20a is set to form an angle of 0 or 90 degrees
with respect to a polarization plane of the incident P-polarized light
(polarized in the Z direction), the P-polarized light (polarized in the Z
direction) that enters the crystal prism 20a is transmitted through the
crystal prism 20a as P-polarized light without changing the polarization
plane, and the mask M is illuminated by the light in the P-polarized
state (polarized in the Y direction) that is transmitted through the
quartz prism 20a.

[0120] On the other hand, if the crystal optic axis of the half-wave plate
10 is set to form an angle of 45 degrees with respect to a polarization
plane of the incident P-polarized light, the polarization plane for the
P-polarized light (polarized in the Z direction) that enters the
half-wave plate 10 changes by 90 degrees and enters the crystal prism 20a
as it becomes the S-polarized light (polarized in the X direction). At
this time, if the crystal optic axis of the crystal prism 20a is set to
form an angle of 45 degrees with respect to a polarization plane of the
incident P-polarized light (polarized in the Z direction), the
S-polarized light (polarized in the X direction) that enters the crystal
prism 20a is converted into light in the nonpolarized state and
illuminates the mask M in the nonpolarized state through the silica prism
20b. If the crystal optic axis of the crystal prism 20a is set to form an
angle of 0 or 90 degrees with respect to a polarization plane of the
incident S-polarized light (polarized in the X direction), the
S-polarized light (polarized in the X direction) that enters the crystal
prism 20a is transmitted as is as S-polarized light (polarized in the X
direction) without the polarization plane being changed and illuminates
the mask as S-polarized light (polarized in the X direction) through the
silica prism 20b.

[0121] As described above, in the first exemplary modification of FIG. 5,
the polarized state for the light that illuminates the mask is changed
between the linearly polarized state and the nonpolarized state by
combining the rotation of the half-wave plate 10 about the optical axis
AX and the rotation of the crystal prism 20a about the optical axis AX.
When illuminating the mask M with the linearly polarized light, the
polarized state may be changed between the P-polarized state and the
S-polarized state. Moreover, the half-wave plate 10 and the depolarizer
20 are also positioned on the light source side and the mask side,
respectively, in the first exemplary modification shown in FIG. 5. The
same optical effects and functions may be achieved by positioning the
depolarizer 20 and the half-wave plate 10 on the light source side and
the mask side, respectively.

[0122] FIG. 6 is a diagram schematically showing a polarized state
switching device according to a second exemplary modification. The
polarized state switching device according to the second modification
shown in FIG. 6 has a structure similar to that of the polarized state
switching device according to the embodiment shown in FIG. 4. However, in
contrast with the embodiment in FIG. 4, in which the depolarizer 20 is
structured to be removable from the illumination light path, the second
exemplary modification shown in FIG. 6 is basically different in that the
depolarizer 20 is fixedly positioned in the illumination light path. The
second exemplary modification shown in FIG. 6 is explained below,
focusing on the differences from the embodiment shown in FIG. 4.

[0123] In the second exemplary modification, the crystal optic axis of the
crystal prism 20a is positioned to form an angle of 0 or 90 degrees with
respect to a polarization plane of the incident P-polarized light
(polarized in the Z direction). Therefore, if the crystal optic axis of
the half-wave plate 10 is set to form an angle of 0 or 90 degrees with
respect to a polarization plane of the incident P-polarized light
(polarized in the Z direction), the P-polarized light (polarized in the Z
direction) that enters the half-wave plate 10 is transmitted through the
half-wave plate 10 as is as P-polarized light (polarized in the Z
direction) and enters the crystal prism 20a, without its polarization
plane being changed. Because the crystal optic axis of the crystal prism
20a is fixedly positioned to form an angle of 0 or 90 degrees with
respect to a polarization plane of the incident P-polarized light
(polarized in the Z direction), the P-polarized light (polarized in the Z
direction) that enters the crystal prism 20a is transmitted through the
crystal prism 20a as is as P-polarized light (polarized in the Z
direction) without changing the angle of the polarization plane, and
illuminates the mask M as P polarized light (polarized in the Y
direction) through the silica prism 20b.

[0124] Moreover, if the crystal optic axis of the half-wave plate 10 is
set to form an angle of 0 or 90 degrees with respect to a polarization
plane of the incident P-polarized light (polarized in the Z direction),
the polarization plane for the P-polarized light (polarized in the Z
direction) that enters the half-wave plate 10 is changed by 90 degrees,
and the light enters the crystal prism 20a as S-polarized light
(polarized in the X direction). Because the crystal optic axis of the
crystal prism 20a is positioned to form an angle of 0 or 90 degrees with
respect also to a polarization plane of the incident S-polarized light
(polarized in the X direction), the S-polarized light (polarized in the X
direction) that enters the crystal prism 20a is transmitted through the
crystal prism 20a as is as S-polarized light (polarized in the X
direction) without changing the angle of the polarization plane and
illuminates the mask M as S-polarized light (polarized in the X
direction) through the silica prism 20b.

[0125] Further, if the crystal optic axis of the half-wave plate 10 is set
to form an angle of 22.5 degrees with respect to a polarization plane of
the incident P-polarized light (polarized in the Z direction), the
polarization plane for the P-polarized light that enters the half-wave
plate 10 enters the crystal prism 20a after being converted into light in
the nonpolarized state that includes a P-polarized component (polarized
in the Z direction), in which the polarization plane for the light
transmitted as is without any change, and an S-polarized component
(polarized in the X direction), in which the angle of the polarization
plane is changed by 90 degrees. Because the crystal optic axis of the
crystal prism 20a is positioned to form an angle of 0 or 90 degrees with
respect also to the polarization plane of the incident P-polarized
component as well as to the polarization plane of the incident
S-polarized light (polarized in the X direction), the P-polarized light
(polarized in the Z direction) and the S-polarized light (polarized in
the X direction) that enters the crystal prism 20a are transmitted
through the crystal prism 20a as is without changing the angle of the
polarization plane and illuminate the mask M in the nonpolarized state
through the silica prism 20b.

[0126] As described above, in the second exemplary modification shown in
FIG. 6, by appropriately rotating the half-wave plate 10 about the
optical axis AX with the depolarizer 20 being fixedly positioned in the
illumination light path, the polarized state for the light that
illuminates the mask M may be switched between the linearly polarized
state and the nonpolarized state, and if illuminating the mask with the
linearly polarized light, the polarized state may be changed between the
P-polarized state and the S-polarized state. In addition, in the second
exemplary modification shown in FIG. 6, the half-wave plate 10 and the
depolarizer 20 are also positioned on the light source side and the mask
side, respectively. However, the same optical functions and effects may
be obtained even if the depolarizer 20 is positioned on the light source
side, and the half-wave plate 10 is positioned on the mask side.

[0127] FIG. 7 is a diagram schematically showing a structure of a
polarized state switching device according to a third exemplary
modification. The polarized state switching device according to the third
exemplary modification shown in FIG. 7 has a structure similar to the
polarized state switching device according to the first exemplary
modification shown in FIG. 5. However, in contrast with the first
exemplary modification in FIG. 5, in which the polarized state switching
device is structured from the half-wave plate 10 and the depolarizer 20,
the third exemplary modification shown in FIG. 7 is basically different
in that the polarized state switching device is structured from only the
depolarizer 20 that is rotatable about the optical axis AX. The third
exemplary modification shown in FIG. 7 is explained below, focusing on
the differences from the first exemplary modification shown in FIG. 5.

[0128] In the third exemplary modification, if the crystal optic axis of
the crystal prism 20a is set to form an angle of 45 degrees with respect
to a polarization plane of the incident P-polarized light (polarized in
the Z direction), the P-polarized light that enters the crystal prism 20a
is converted into light in the nonpolarized light and illuminates the
mask M in the nonpolarized state through the silica prism 20b. On the
other hand, if the crystal optic axis of the crystal prism 20a is set to
form an angle of 0 or 90 degrees with respect to a polarization plane of
the incident P-polarized light (polarized in the Z direction), the
P-polarized light (polarized in the Z direction) that enters the crystal
prism 20a is transmitted through the crystal prism 20a as is as
P-polarized light (polarized in the Z direction) without changing the
polarization plane and illuminates the mask M in the P-polarized state
(polarized in the Y direction) through the silica prism 20b.

[0129] As described above, in the third exemplary modification shown in
FIG. 7, by appropriately rotating the crystal prism 20a about the optical
axis AX, the polarized state for the light that illuminates the mask M
may be switched between the linearly polarized state and the nonpolarized
state. Moreover, in the third exemplary modification shown in FIG. 7, the
same optical operational effects may be obtained by structuring the
depolarizer 20 to be rotatable about the optical axis AX and removable
from the illumination light path and by setting the depolarizer 20 to be
removed from the illumination light path to allow illumination of the
mask M in the P-polarized state.

[0130]FIG. 8 is a diagram schematically showing a structure of the
depolarizer according to an exemplary modification. In the
above-described embodiment and first-third exemplary modifications, the
depolarizer 20 adapts a structure having the crystal prism 20a. However,
as shown in the exemplary modification shown in FIG. 8, the depolarizer
21 may be structured from a polarized beam splitter 21a and a reflection
system (21b-21e). According to FIG. 8, the depolarizer 21 is equipped
with the polarized beam splitter 21a positioned in the illumination light
path. Of the light that enters the polarized beam splitter 21a, the
P-polarized light (polarization directions indicated by bidirectional
arrows in the figure) with respect to a polarization separation surface
of the polarized beam splitter 21a is transmitted through the polarized
beam splitter 21a.

[0131] On the other hand, the S-polarized light (polarization direction
indicated by dots in the figure) with respect to the polarization
separation surface of the polarized beam splitter 21a is, after being
reflected by the polarized beam splitter 21 a, returned to the polarized
beam splitter 21a as light that has been reflected four times in a plane
parallel to the surface of FIG. 8 by actions of the reflection system
structured from four reflection mirrors 21b-21e. The reflection system
(21b-21e) is structured such that the path of the P-polarized light that
is transmitted through the polarized beam splitter 21a and the path of
the S-polarized light that is eventually reflected by the polarized beam
splitter 21a substantially match each other. As a result, the P-polarized
light that is transmitted through the polarized beam splitter 21a and the
S-polarized light that is eventually reflected by the polarized beam
splitter 21a are ejected from the depolarizer 21 substantially on the
same light path. However, the S-polarized light is delayed compared to
the P-polarized light by the length of the light path created by the
reflection system (21b-21e).

[0132] The depolarizer 21 structured from the polarized beam splitter 21a
and the reflection system (21b-21e) has optical functions that are
basically equivalent to those of the depolarizer 20 structured from the
crystal prism 20a and the silica prism 20b. Therefore, the depolarizer 20
in the exemplary embodiment and the first to third exemplary
modifications may be replaced with the depolarizer 21 according to the
exemplary modification shown in FIG. 8. That is, when using the
depolarizer 21 in the exemplary embodiment shown in FIG. , the polarized
beam splitter 21a and the reflection system (21b-21e) may be structured
to be integrally insertable into and removable from the illumination
light path.

[0133] When using the depolarizer 21 in the first exemplary modification
shown in FIG. 5 or the third exemplary modification shown in FIG. 7, the
polarized beam splitter 21a and the reflection system (21b-21e) may be
structured to be integrally rotatable about the optical axis AX.
Furthermore, when using the depolarizer 21 in the second exemplary
modification shown in FIG. 6, the polarized beam splitter 21a and the
reflection system (21b-21e) may be positioned fixedly in the illumination
light path.

[0134] By using the depolarizer 21 according to the exemplary embodiment
shown in FIG. 8, the coherency of the laser beam that illuminates the
mask M may be reduced, and therefore, a speckle contrast on the wafer may
be reduced, by setting the length of the light path on the reflection
system (21b-21e) substantially longer than a coherence length. Detailed
structures of and various examples of modifications for a depolarizer,
which has a polarized beam splitter and a reflection system and are
adaptable in this invention, are described in Japanese Laid-Open Patent
application Ser. No. 11-174365, Japanese Laid-Open Patent Application No.
11-312631, Japanese Laid-Open Patent Application No. 2000-223396 and U.S.
Pat. No. 6,238,063. The disclosure of U.S. Pat. No. 6,238,063 is
incorporated herein by reference in its entirety.

[0135] FIG. 9 is a diagram schematically showing an internal structure for
a beam matching unit positioned between the light source and the
polarized state switching device shown in FIG. 1. In the beam matching
unit BMU shown in FIG. 9, the beam with parallel light rays provided from
the laser light source 1 (e.g., KrF excimer laser light source or ArF
excimer laser light source) enters the beam expander 2 after being
transmitted through a pair of deviation prisms 31 and a plane parallel
plate 32. The laser light source 1 may be provided on a base plate A on a
lower level, for example.

[0136] One of the pair of deviation prisms 31 is structured to be
rotatable about the optical axis AX. Therefore, by relatively rotating
the pair of deviation prisms 31 about the optical axis AX, the angle of
the beam with parallel light rays with respect to the optical axis AX may
be adjusted. That is, the pair of deviation prisms 31 forms a beam angle
adjustment device for adjusting an angle of the beam with parallel light
rays provided from the laser light source 1 with respect to the optical
axis AX. In addition, the plane parallel plate 32 is structured to be
rotatable about two axes that are orthogonal to each other and that
extend in a plane perpendicular to the optical axis AX.

[0137] Accordingly, by rotating the plane parallel plate 32 about each of
the axes to incline the plane parallel plate 32 with respect to the
optical axis AX, the beam with parallel light rays can be moved in
parallel to the optical axis AX. That is, the plane parallel plate 32
forms a beam parallel movement device for moving the beam with parallel
light rays provided from the laser light source 1 in parallel to the
optical axis AX. As a result, the beam with parallel light rays from the
light source 1, which is transmitted through the pair of deviation prisms
31 and the plane parallel plate 32, enters a first rectangular prism 33
after being expanded and formed into a beam with parallel light rays
having a predetermined cross-sectional shape through the beam expander 2.

[0138] The beam with parallel light rays deflected in a vertical direction
by the first rectangular prism 33, which functions as a back surface
reflection mirror, enters a sixth rectangular prism 38 as a beam with
parallel light rays after passing through an opening on the base plate
Bon an upper level, after being sequentially reflected by the second
rectangular prism 34 to the fifth rectangular prism 37, which also
function as back surface reflection mirrors. As shown in FIG. 9, the
second rectangular prism 34 to the fifth rectangular prism 37 are
arranged in such a manner that the beam with parallel light rays
deflected in the vertical direction by the first rectangular prism 33 to
be directed to the sixth rectangular prism is transmitted around pipes 39
for supplying pure water or ventilating air, for example.

[0139] The beam deflected in a horizontal direction by the sixth
rectangular prism 38, which functions as a back side reflection mirror,
enters a half mirror 40. The beam reflected by the half mirror 40 is lead
to a displacement and inclination detection system 41. On the other hand,
the beam transmitted through the half mirror 40 is lead to a polarized
state switching device 42 formed by the half-wave plate 10 and the
depolarizer 20. By the displacement and inclination detection system 41,
displacement and inclination of the beam with parallel light rays that
enters the polarized state switching device 42 (and subsequently the
diffractive optical element , which functions as an optical integrator),
is detected with respect to the optical axis AX.

[0140] If, for example, the ArF excimer laser light source is used as the
laser light source 1, it is generally the case that a required durability
is secured for light transmissive members that receive illumination of
light having high energy density by using fluorite for those members. In
this case, as described below, the polarization plane for the linearly
polarized light may change in a short or long term when the light is
transmitted through the light transmissive members formed by fluorite. If
the polarization plane for the linearly polarized light is changed by the
light transmissive members formed by fluorite, the crystal prism 20a does
not function as the nonpolarized element.

[0141]FIG. 10 is a diagram explaining the crystal orientation of
fluorite. As shown in FIG. 10, the crystal orientation of fluorite is
described with reference to the cubic crystal axes a1, a2 and
a3. That is, crystal orientations [100], [010] and [001] are
provided along the orientation axes +a1, +a2 and +a3,
respectively. In addition, a crystal orientation [101] is provided in a
direction extending 45 degrees from the crystal orientations [100] and
[001] in the a1 a3 plane. A crystal orientation [110] is
provided in a direction extending 45 degrees from the crystal
orientations [100] and [010] in the a1a2 plane. A crystal
orientation [011] is provided in a direction extending 45 degrees from
the crystal orientations [010] and [001] in the a2a3 plane.
Furthermore, a crystal orientation [111] is provided in a direction
forming equivalent acute angles with respect to the crystal axes
+a1, +a2 and +a3. In FIG. 10, only crystal orientations in
a space are provided by the crystal axes +a1, +a2 and +a3.
However, similar crystal orientations may be provided in other spaces.

[0142] As verified by applicants, the polarization plane for the linearly
polarized light is not substantially changed by the light transmissive
members formed by fluorite as long as the traveling direction of the
light is substantially matched with the crystal orientation [111] or a
crystal orientation equivalent thereto in the crystal structure.
Similarly, the polarization plane for the linearly polarized light is not
substantially changed by the light transmissive members formed by
fluorite as long as the traveling direction of the light is substantially
matched with the crystal orientation [100] or a crystal orientation
equivalent thereto in the crystal structure. On the other hand, if the
traveling direction of the light is substantially matched with the
crystal orientation [110] or a crystal orientation equivalent thereto in
the crystal structure, the polarization plane for the linearly polarized
light is changed through the light transmissive member formed by fluorite
in a short or long term.

[0143] In this specification, "a crystal orientation equivalent to a
certain crystal orientation in the crystal structure" device a crystal
orientation equivalent in the crystal structure to a crystal orientation
in which indexes for the crystal orientation is reordered and in which
signs for at least a part of the indexes are reversed, that is, when the
crystal orientation is [uvw], then equivalent orientations are [uwv],
[vuw], [vwu], [wuv], [wvu], [-uvw], [-uwv], [-vuw], [-vwu], [-wuv],
[-wvu], [u-vw], [u-wv], [v-uw], [v-wu], [w-uv], [w-vu], [uv-w], [uw-v],
[vu-w], [vw-u], [wu-v], [wv-u], [-u-vw], [-u-wv], [-uv-w], [-uw-v],
[-v-uw], [-v-wu], [-vu-w], [-vw-u], [-w-uv], [-w-vu], [-wu-v], [-wv-u],
[u-v-w], [u-w-v], [v-u-w], [v-w-u], [w-u-v], [w-v-u], [-u-v-w], [-u-w-v],
[-v-u-w], [-v-w-u], [-w-u-v], and [-w-v-u]. Moreover, in this
specification, the crystal orientation [uvw] and the crystal orientations
equivalent to the crystal orientation [uvw] in the crystal structure is
referred to as a crystal orientation <uvw>. Furthermore, a plane
orthogonal to the crystal orientation [uvw] and the crystal orientation
equivalent to the crystal orientation [uvw] in the crystal structure, is
referred to as a crystal plane (uvw), and a crystal plane equivalent to
the crystal plane (uvw) in the crystal structure is referred to as a
crystal plane {uvw}.

[0144] In this exemplary embodiment, the traveling direction of the light
is configured to be closer to the crystal orientations <111> and
<100> than to the crystal orientation <110> in the light
transmissive member formed by fluorite that is positioned in the light
path between the laser light source 1 and the polarized state switching
device 42. In detail, if the optical member, such as lens components (2a,
2b) that form the beam expander 2, securely positioned in the light path
is formed by fluorite, the optical axis of the optical member is
configured to substantially match the crystal orientation <111> or
<100>.

[0145] In this case, because the laser light is transmitted substantially
along the crystal orientation <111> or <100>, the
polarization plane for the linearly polarized light that is transmitted
through the lens components (2a, 2b) is not changed substantially.
Similarly, if the pair of deviation prisms 31 is formed by fluorite,
changes in the polarization plane for the transmitted linearly polarized
light may be substantially avoided by configuring the optical axis of the
pair of the deviation prisms 31 substantially match the crystal
orientation <111> or <100>.

[0146] Moreover, if the rectangular prisms 33-38, which function as back
surface reflection mirrors, are formed by fluorite, an incident surface
and an exit surface of the rectangular prisms 33-38 are configured to
substantially match the crystal plane {100}, and reflection surfaces of
the rectangular prisms 33-38 are configured to substantially match the
crystal plane {110}. In such a case, because the laser beam is
transmitted substantially along the crystal orientation <100>, the
polarization plane for the linearly polarized light transmitted through
the rectangular prisms 33-38 does not substantially change.

[0147] Furthermore, if the plane parallel plate 32, which functions as the
beam parallel movement device, that is provided in the light path
inclineably with respect to the optical axis AX and that moves in
parallel the light beam incident along the optical axis AX, is formed by
fluorite, the optical axis of the plane parallel plate 32 is configured
to substantially match with the crystal orientation <100>. This is
because the crystal orientations <100> and <110> form an
angle of 45 degrees, while the crystal orientations <111> and
<110> form an angle of about 35 degrees.

[0148] If the optical axis of the plane parallel plate 32 is substantially
matched with the crystal orientation <111>, that is, substantially
matched with the crystal plane {111} of the optical plane thereof, the
traveling direction of the laser light transmitted through the plane
parallel plate 32 comes close to the crystal orientation <110> when
the plane parallel plate 32 is inclined at the maximum level (e.g., about
32 degrees) with respect to the optical axis AX. However, if the optical
axis of the plane parallel plate 32 is substantially matched with the
crystal orientation <100>, that is, if the optical plane thereof is
substantially matched with the crystal plane {100}, a condition in which
the traveling direction of the laser light transmitted through the plane
parallel plate 32 is away from the crystal orientation <110> at
some level, may be secured even when the plane parallel plate 32 is
inclined at the maximum level (e.g., about 32 degrees) with respect to
the optical axis AX. As a result, by substantially matching the optical
axis of the plane parallel plate 32 with the crystal orientation
<100>, changes in the polarization plane for the linearly polarized
light transmitted through the plane parallel plate 32 may be avoided
regardless of the position of the plane parallel plate.

[0149] In the above descriptions, the traveling direction of the light is
configured to come closer to the crystal orientation <111> or
<100> than to the crystal orientation <110> to avoid changes
in the polarization plane for the linearly polarized light transmitted
through the light transmissive member positioned in the light path
between the laser light source 1 and the polarized state switching
device. However, the invention is not limited to this. Similar
configurations may be implemented for the light transmissive member
positioned in the light path between the polarized state switching device
42 and the mask M, which is an illuminated body (and therefore the wafer
W), such that the changes in the polarization plane for the linearly
polarized light that originate in fluorite may be avoided throughout the
entire illumination light path.

[0150] Moreover, in the above descriptions, the traveling direction of the
light is configured to be closer to the crystal orientations <111>
or <100> than to the crystal orientation <110> in order to
avoid changes in the polarization plane for the linearly polarized light
transmitted through the light transmissive member formed by fluorite.
However, the invention is not limited to fluorite. Similar configuration
may be implemented for a light transmissive member formed by a cubic
system crystal material, such as calcium fluoride, barium fluoride, and
magnesium fluoride, to avoid changes in the polarization plane for the
linearly polarized light originated in such a crystal material.

[0151] A plurality of rectangular prisms 33-38 (there are 6 in FIG. 9 as
an example) are provided for the beam matching unit BMU shown in FIG. 9.
In general, even if the laser light source 1 is a KrF excimer laser light
source or an ArF excimer laser light source, the linearly polarized light
is changed to elliptically polarized light due to the total reflection by
the rectangular prisms that function as back surface reflection mirrors
when linearly polarized light enters the rectangular prisms, if the
polarization plane for the incident linearly polarized light does not
match the P-polarization plane or the S-polarization plane (if the
incident linearly polarized light is not P-polarized or S-polarized with
respect to the reflection surface). The polarized state switching device
42 in the exemplary embodiment functions under the assumption that
linearly polarized light is entering it, and thus may not achieve the
desired functions if elliptically polarized light enters.

[0152] In the exemplary embodiment, as shown in FIG. 11, it may be
preferable to additionally provide a quarter-wave plate 11 as a second
phase member for converting the incident elliptically polarized light
into linearly polarized light, on the light source side (left side in
FIG. 11) of the half-wave plate 10 in the polarized state switching
device 42. The quarter-wave plate 11 may be structured with its crystal
optic axis being rotatable about the optical axis AX, for example. In
this case, by configuring the crystal optic axis for the 1/4 wavelength
11 in accordance with the characteristics of the incident elliptically
polarized light, the linearly polarized light enters the half-wave plate
10 to maintain the proper functions of the polarized state switching
device 42, even if elliptically polarized light originating from the
rectangular prism, for example, enters the polarized state switching
device 42. In FIG. 11, the quarter-wave plate 11 is positioned on the
light source side of the half-wave plate 10. However, the quarter-wave
plate 11 may be positioned on the mask side (right side in FIG. 11) of
the half-wave plate.

[0153] In the above descriptions, a method for avoiding changes in the
polarization plane for linearly polarized light that is transmitted
through the light transmissive members formed with fluorite, and a method
for maintaining the proper functioning of the polarized state switching
device even if elliptically polarized light enters the polarized state
switching device as a result of the rectangular prisms, is applied in the
embodiments shown in FIGS. 1-4. However, the invention is not limited to
these embodiments. These methods may be applied similarly to the
exemplary modifications of FIGS. 5-8.

[0154] Moreover, in the above descriptions, to avoid changes in the
polarization plane (changes in polarized state) for the linearly
polarized light that is transmitted through the light transmissive
members formed with a cubic system crystal material, such as fluorite,
the crystal orientation of such a crystal material is taken into account.
Instead of or in addition to this method, the light transmissive members
formed by the cubic system crystal material may be kinematically held by
using the method disclosed in U.S. Patent Publication US2002/0163741A (or
WO02/16993), each of which is incorporated herein by reference in its
entirety. As a result, even if the light transmissive members expand due
to heat generated when the light having high energy density is
transmitted through the light transmissive members formed with the cubic
system crystal material, such as fluorite, generation of applied double
refraction that occurs in the light transmissive members may be
controlled, and changes in the polarization plane (changes in the
polarized state) for the linearly polarized light that is transmitted
though the light transmissive members may be controlled.

[0155] Next, improvement of image forming characteristics for the
projection optical system (e.g., depth of focus and resolution) to
perform well and accurate transferring of the mask pattern by
illuminating the mask with the light having a predetermined polarized
state for different types of mask patterns is described in detail using
examples. First, for dipole illumination (generally, illumination that
forms two separated areas having a high light intensity distribution near
or adjacent to the pupil plane), for example, the image forming
characteristics of the projection optical system for a mask pattern 141
can be improved by forming two planar light sources 142a and 142b that
are spaced away from each other in the pitch direction (X direction:
corresponding to the X direction on the mask) of a line-and-space pattern
141 formed on the mask as shown in FIG. 14, and by illuminating the mask
with light in the linearly polarized state that has polarization planes
(indicated by bi-directional arrows Fl in the figure) in a direction (Y
direction: corresponding to the Z direction on the pupil plane)
orthogonal to the direction (X direction: corresponding to the X
direction on the pupil plane) in which the two planar light sources 142a
and 142b are spaced away from each other. For a two-dimensional mask
pattern, in which patterns in the vertical direction and patterns in the
horizontal direction are mixed, the pattern transfer may be performed at
high throughput by illuminating the mask with light in the nonpolarized
state, without generating line width problems between the patterns in the
vertical direction and the patterns in the horizontal direction.

[0156] To sufficiently improve the image forming characteristics for the
projection optical system under the above-described dipole illumination,
it is preferable to form the two planar light sources 142a and 142b
symmetrically about the optical axis AX and to satisfy the following
condition (1):

0.7≦σo (1)

[0157] For the condition (1), σo is a value (normally called an
outside σ) defined by φ/φp. As shown in FIG. 14, φo is
a diameter of a circle circumscribing the two planar light sources 142a
and 142b about the optical axis AX, and φp is a diameter of a pupil
plane 143. To further improve the image forming characteristics of the
projection optical system, it is preferable to set the lower value of the
condition (1) at 0.9.

[0158] Moreover, to sufficiently improve the image forming characteristics
of the projection optical system under the above-described dipole
illumination, it is preferable to form the two planar light sources 142a
and 142b symmetrically about the optical axis AX and to satisfy the
following condition (2):

0.5≦σi/σo (2)

[0159] For the condition (2), of is a value (normally called an inside a)
defined by φi/φp, and σo is the outside σ defined by
φo/φp. As shown in FIG. 14, σi is a diameter of a circle
inscribing the two planar light sources 142a and 142b about the optical
axis AX. To further improve the image forming characteristics of the
projection optical system, it is preferable to set the lower value of the
condition (2) at 0.67 (≈2/3).

[0160] Next, for the circular illumination (generally, illumination that
forms one area having a high light intensity distribution, having a
center that is substantially on the optical axis on or adjacent to the
pupil plane), for example, the image forming characteristics of the
projection optical system with respect to the mask pattern 151 may be
improved by using a phase shift mask as the mask and by illuminating the
mask with the light in the linearly polarized state that has the
polarization plane in the direction (Y direction: corresponding to the Z
direction on the pupil plane) orthogonal to the pitch direction (X
direction: corresponding to the X direction on the mask) of the
line-and-space pattern 151 formed on the phase shift mask, as shown in
FIG. 15. In addition, in the circular illumination, similar to the case
of the dipole illumination, the pattern may be transferred at high
throughput by illuminating the mask with the light in the nonpolarized
state, for example.

[0161] In particular, to sufficiently improve the image forming
characteristics of the projection optical system in the above-described
circular illumination, it is preferable to meet the following condition
(3).

σ≦0.4 (3)

[0162] In the condition (3), σ a value (normally called a value
σ) defined by φ/φp. As shown in FIG. 15, φ is a
diameter of a circular planar light source 152 (generally the size of the
area with a high light intensity distribution), and φp is a diameter
of the pupil plane 153 as described above. To further improve the image
forming characteristics of the projection optical system, it is
preferable to set the upper limit value for the condition (3) at 0.3.

[0163] Next, conditions that the light that is substantially in the
linearly polarized state or substantially in the nonpolarized state
should satisfy for this invention are described. First, it is preferable
that component S1 of the Stokes parameter for the light that is
substantially in the linearly polarized state herein, satisfies the
following condition (4):

0.6≦|S1| (4)

[0164] In addition, it is preferable that components S1 and S2 of the
Stokes parameter for the light that is substantially in the nonpolarized
state herein, satisfy the following conditions (5) and (6):

|S1|≦0.1 (5)

|S2|≦0.1 (6)

[0165] To make the light that is substantially in the linearly polarized
state sufficiently closer to being linearly polarized, it is preferable
to set the lower limit value of the condition (4) at 0.8. For example, if
an ArF excimer laser that provides light with a wavelength of 193 nm is
used as the light source, and if a numerical aperture for the projection
optical system PL on the image side is 0.92, a depth of focus DOF (166
nm) in the nonpolarized state may be improved to a depth of focus DOF
(202 nm) for the vertical patterns, with an exposure amount error of 2%
and a line width error of ±10% when φo and σi are set to
0.93 and 0.73, respectively, in the dipole illumination shown in FIG. 14
using a 6% halftone reticle (mask error: ±2 nm) having a
line-and-space pattern at 65 nm. If the condition (4), that is, the
degree of polarization, exceeds 0.8, the change in line width due to
changes in the degree of polarization may be substantially ignored. In
the above-described conditions, the generated line width difference is
only 0.2 nm between the degrees of polarization of 0.8 (|S1|=0.8) and 1.0
(|S1|=1.0). This difference may be substantially ignored. In other words,
the values for the condition (4) may fluctuate in the range of the degree
of polarization between 0.8 and 1.0.

[0166] Moreover, to make the light substantially in the nonpolarized state
closer to the sufficiently nonpolarized light, it is preferable to set
the upper values for both of the conditions (5) and (6) at 0.04. If the
conditions (5) and (6), that is, the degrees of polarization, are lower
than 0.1, the line width difference due to the polarization may be
reduced to less than 2 nm (the value σ is set at 0.2 (small σ
illumination) in the circular illumination shown in FIG. 15 using a phase
shift mask having patterns isolated by 50 nm, with the light source
wavelength of 193 nm and the image-side numerical aperture for the
projection optical system PL at 0.78). If the conditions (5) and (6),
that is, the degrees of polarization, are lower than 0.4, the line width
difference due to the polarization under the above-described conditions
may be reduced lower than 0.7 nm. Moreover, for the conditions (5) and
(6), even if the degree of polarization is high when microscopically
viewing the area in the planar light source, the light is considered to
be substantially nonpolarized if the polarized state changes with minute
frequency within the area. Therefore, for calculating the polarization
degree distribution in the planar light source, a moving average may be
used in an area of a size where the value σ becomes 0.1.

[0167] For the circular and annular illuminations, differences in the
pattern line width are generated between the vertical and horizontal
directions if a desired nonpolarized state, in which the degree of
remaining polarization is sufficiently low, is not achieved. In addition,
for the dipole illumination, for example, improvement of the image
forming characteristics for patterns with a narrow line width having a
predetermined pitch direction may not be accomplished if the desired
linearly polarized state that has the polarization plane in a
predetermined direction is not achieved. Therefore, in the exemplary
modification of this embodiment, a polarization monitor is provided to
detect the polarized state of the light that illuminates the mask M as
the illuminated surface (and therefore also the wafer W).

[0168] FIG. 16 is a diagram schematically showing a structure of the
exposure apparatus shown in FIG. 1 that is additionally provided with a
polarization monitor for detecting the polarized state of the
illumination light. In the exposure apparatus according to an exemplary
modification shown in FIG. 16, the structure between the micro lens array
8 and the mask M is different from that of the exposure apparatus shown
in FIG. 1. That is, in this exemplary modification, the light beam from
the secondary light source (generally, a predetermined light intensity
distribution formed on or adjacent to the pupil plane of the illumination
optical system) formed on the rear focal plane of the micro lens array
illuminates superimposingly a mask blind MB after being transmitted
through a beam splitter 51 and a condenser optical system 9a.

[0169] Accordingly, a rectangular illumination field corresponding to the
shape and focal length of each micro lens forming the micro lens array 8
is formed on the mask blind MB that functions as an illumination field
diaphragm. Internal structures and functions of the polarization monitor
50 that includes a beam splitter 51 will described later. The light beam
transmitted through the rectangular opening (light transmissive part) of
the mask blind MB illuminates superimposingly the mask M, on which a
predetermined pattern is formed, after being converged by the image
forming optical system 9b. As a result, the image forming optical system
9b forms an image of the rectangular opening of the mask blind MB on the
mask M.

[0170] Moreover, in the exposure apparatus according to the exemplary
modification shown in FIG. 16, the structures between the folding mirror
3 and the diffractive optical element are different from those in the
exposure apparatus shown in FIG. 1. That is, in this exemplary
modification, the polarized state switching device (quarter-wave plate
11, half-wave plate 10 and depolarizer 20) shown in FIG. 11 is provided
instead of the polarized state switching device (half-wave plate 10 and
the depolarizer 20) shown in FIG. 1. As described below, the output of
the polarization monitor 50 is supplied to a control system 70. In
addition, the control system 70 drives the polarized state switching
device (11, 10, 20) via a drive system 71. In the polarized state
switching device having the structure shown in FIG. 11, an additional
quarter-wave plate may be used instead of the half-wave plate 10.

[0171]FIG. 17 is a perspective diagram schematically showing an internal
structure of the polarization monitor shown in FIG. 16. In FIG. 17, the
polarization monitor 50 is provided with the first beam splitter 51
positioned in the light path between the micro lens array 8 and the
condenser optical system 9a. The first beam splitter 51 has a form of an
uncoated plane parallel plate (i.e., bare glass) formed by a silica glass
and has a function to extract from the light path the reflected light
having a polarized state different from the polarized state of the
incident light.

[0172] The light extracted by the first beam splitter 51 from the light
path enters the second beam splitter 52. Similar to the first beam
splitter 51, the second beam splitter 52 has a form of an uncoated plane
parallel plate formed by silica glass, for example, and has a function to
generate the reflected light in a polarized state different from the
polarized state of the incident light. The first beam splitter 51 and the
second beam splitter 52 are configured such that P-polarized light for
the first beam splitter becomes S-polarized light for the second beam
splitter, and S-polarized light for the first beam splitter 51 becomes
P-polarized light for the second beam splitter.

[0173] The light transmitted through the second beam splitter 52 is
detected by the first light intensity detector 53. The light reflected by
the second beam splitter 52 is detected by the second light intensity
detector 54. The outputs from the first light intensity detector 53 and
the second light intensity detector 54 are both supplied to the control
system 70. As discussed above, the control system 70 drives the
quarter-wave plate 11, the half-wave plate, and the depolarizer 20, which
form the polarized state switching device, via the drive system 71 as
needed.

[0174] As described above, the reflectivity for P-polarized light and the
reflectivity for S-polarized light are substantially different for the
first beam splitter 51 and the second beam splitter 52. Therefore, in the
polarization monitor 50, the light reflected from the first beam splitter
51 includes the S-polarized component of approximately 10% of the light
incident to the first beam splitter 51 (S-polarization for the first beam
splitter, which is the P-polarized component for the second beam
splitter), for example, and the P-polarized component of approximately 1%
of the light incident to the first beam splitter (P-polarization for the
first beam splitter, which is the S-polarized component for the second
beam splitter), for example.

[0175] Moreover, the light reflected from the second beam splitter 52
includes the P-polarized component of approximately 0.1%, which is 1% of
the 10% of the light incident to the first beam splitter 51
(P-polarization for the first beam splitter, which is the S-polarized
component for the second beam splitter), for example, and the S-polarized
component of approximately 0.1%, which is 1% of the 10% of the light
incident to the first beam splitter (S-polarization for the first beam
splitter, which is the P-polarized component for the second beam
splitter), for example.

[0176] Accordingly, in the polarization monitor, the first beam splitter
51 functions to extract from the light path the reflected light in a
polarized state that is different from the polarized state of the
incident light. As a result, although there is a slight effect by changes
in polarization due to the polarization characteristics of the second
beam splitter, the polarized state (degree of polarization) of the light
incident to the first beam splitter 51, and thus the polarized state of
the light illuminating the mask M, may be detected based on the output of
the first light intensity detector 53 (information related to the
strength of the light transmitted through the second beam splitter, that
is, the information related to the intensity of the light in the
polarized state that is substantially the same as that for the light
reflected from the first beam splitter 51).

[0177] Furthermore, in the polarization monitor 50, the P-polarized light
and the S-polarized light for the first beam splitter are configured to
be S-polarized light and P-polarized light for the second beam splitter,
respectively. As a result, the amount (intensity) of the light incident
to the first beam splitter, and thus of the light illuminating the mask
M, may be detected based on the output of the second light intensity
detector 54 (information related to the intensity of the light
sequentially reflected by the first beam splitter 51 and the second beam
splitter 52), without being substantially affected by the changes in the
polarized state for the light incident to the first beam splitter.

[0178] As such, using the polarization monitor 50, the polarized state of
the light incident to the first beam splitter 51 may be detected, and
thus a determination may be subsequently made as to whether the light
illuminating the mask M is in the desired nonpolarized state or linearly
polarized state. In addition, when the control system 70 confirms that,
based on the detection result by the polarization monitor 50 that the
light illuminating the mask M (and subsequently the wafer W) has not been
in the desired nonpolarized state or linearly polarized state, the
quarter-wave plate 11, the half-wave plate 10 and the depolarizer 20,
which form the polarized state switching device, are driven via the drive
system 71 for adjustment, so that the condition of the light illuminating
the mask M may be adjusted to the desired nonpolarized state or linearly
polarized state.

[0179] As described above, the polarization monitor 50, the control system
70, the drive system 71, and the polarized state switching device (11,
10, 20) which has a function to adjust the polarized state on the
illuminated surface, are positioned in the light path between the light
source 1 and the mask M and form a polarized state fluctuation correction
device that corrects the fluctuation of the polarized state on the mask
M. In this case, it is preferable to avoid, as much as possible,
positioning optical members that have characteristics to change and eject
the polarized state of the incident light, such as an optical member
formed by a crystal optical material, such as fluorite that has double
refractivity (birefringence), or a quartz that has optical activity
(rotary polarization, optical rotation), in the light path between the
polarization monitor 50 and the mask M. Moreover, in the light path
between the polarization monitor 50 and the light source 1 also, it is
preferable to avoid, as much as possible, positioning optical members
that have characteristics to change the polarized state of the light that
is ejected. However, to secure the durability of the optical member with
respect to the illumination of light, it may be necessary to consider the
effects from the changes in polarization caused by the optical members,
such as the diffractive optical elements 4 and 6, if such optical members
are formed by fluorite or crystal.

[0180] Furthermore, in the above-descriptions, if the first light
intensity detector 53 is structured such that the light reflected from
the first beam splitter 51 directly enters the first light intensity
detector 53, the polarized state of the light incident to the first beam
splitter 51 may be detected highly accurately without having the output
of the first light intensity detector 53 being affected by the
polarization fluctuation due to the polarization characteristics of the
second beam splitter 52. In addition, without being limited to the
structure shown in FIG. 17, there are various exemplary modifications for
the detailed structure of the polarization monitor 50. Moreover, in the
above description, the polarized state switching device is structured by
the quarter-wave plate 11, the half-wave plate 10 and the depolarizer 20.
However, the polarized state switching device may be structured by the
half-wave plate 10 and the depolarizer 20. In such a case, the control
system 70 drives the half-wave plate 10 and the depolarizer 20 via the
drive system 71 as needed.

[0181] In the above-descriptions, to highly accurately detect the
polarized state of the light incident to the first beam splitter 51, it
is preferable that the first beam splitter 51 and the second beam
splitter 52 have reflective characteristics such that the reflectivity
for the P-polarized light is sufficiently different from the reflectivity
for the S-polarized light. In detail, it is preferable that the first
beam splitter 51 and the second beam splitter 52 have reflective
characteristics such that the P-polarized light intensity Ip and the
S-polarized light intensity Is, which are included in the light reflected
from the first beam splitter 51, satisfy a condition that an intensity
ratio Ip/Is is less than 1/2 (Ip/Is<1/2) or more than 2 (Ip/Is>2).

[0182] In addition, in the above descriptions, beam splitters that have a
form of a plane parallel plate are used to extract the reflected light
from the light path. However, the invention is not limited to this. The
polarized state of the light incident to the beam splitter may be
detected by using a beam splitter that extracts from the light path the
light transmitted in a polarized state different from the polarized state
of the incident light and based on the intensity of the transmitted light
extracted from the light path by the beam splitter. In such a case, it is
preferable that the beam splitter has transmissive characteristics such
that the P-polarized light intensity Ip and the S-polarized light
intensity Is, which are included in the light reflected from the beam
splitter, satisfy a condition that the intensity ratio Ip/Is is less than
1/2 (Ip/Is<1/2) or more than 2 (Ip/Is>2).

[0183] As described above, it is possible that linearly polarized light
from the laser light source 1 is changed to elliptically polarized light
and enters the polarized state switching device (11, 10, 20) due to
effects of the total reflection by the rectangular prisms. In addition,
it is possible that linearly polarized light from the laser light source
1 is changed to elliptically polarized light and enters the polarized
state switching device (11, 10, 20) due to effects by an optical member,
such as one formed by fluorite, which has characteristics to change the
polarized state of the incident light.

[0184] In this case, in order to convert the elliptically polarized state
incident to the quarter-wave plate 11 into linearly polarized light, its
crystal optic axis should be set at a predetermined angular position in
accordance with the orientation of the long axis of the incident
elliptically polarized light. In addition, in order to convert the
linearly polarized light incident to the half-wave plate 10 into linearly
polarized light having a polarization plane in a predetermined direction,
the crystal optic axis should be set at a predetermined angular position
in accordance with the orientation of the polarization plane of the
incident linearly polarized light. A method of adjusting the crystal
optic axis for, the quarter-wave plate and the crystal optic axis for the
half-wave plate is explained before with the polarized state switching
device (11, 10, 20) shown in FIG. 11 as an example. The below adjustment
method may be generally applicable in any optical system equipped with a
half-wave plate and a quarter-wave plate, in which the crystal optic axes
thereof are structured to be rotatable about the optical axis.

[0185]FIG. 18 is a flow chart of a method for adjusting the crystal optic
axes of the quarter-wave plate and of the half-wave plate in the
polarized state switching device shown in FIG. 11. As described in FIG.
18, the depolarizer 20 is removed from the light path, and the crystal
optic axes of the quarter-wave plate 11 and of the half-wave plate 10 are
initially set at the normal angular position, such as -45 degrees (S11).
Next, while the crystal optic axis of the quarter-wave plate 11 is fixed
at the normal angular position of -45 degrees, outputs are obtained from
the polarization monitor 50 at each angular position of the crystal optic
axis of the half-wave plate 10 as the crystal optic axis of the half-wave
plate 10 is rotated by +5 degrees, for example, from the normal angular
position of -45 degrees to an angular position of +45 degrees (S12).

[0186]FIG. 19 is a graph showing the changes in the output of the
polarization monitor at various angular positions of the crystal optic
axis of the half-wave plate. In FIG. 19, the horizontal axis indicates
the angular position (degrees) of the crystal optic axis of the half-wave
plate 10, and the vertical axis indicates the output (values for the
Stokes parameter S1 component) of the polarization monitor 50. Next, as
the crystal optic axis of the quarter-wave plate 11 is rotated by +15
degrees, for example, from the normal angular position of -45 degrees to
an angular position of +45 degrees, outputs from the polarization monitor
50 are obtained at each angular position of the crystal optic axis of the
half-wave plate 10 for each angular position of the crystal optic axis of
the quarter-wave plate 10, as the crystal optic axis of the half-wave
plate 10 is rotated by +5 degrees, for example, from the normal angular
position of -45 degrees to an angular position of +45 degrees (S13).

[0187]FIG. 20 is a graph showing the changes in the output of the
polarization monitor at various angular positions of the crystal optic
axis of the half-wave plate for each angular position of the crystal
optic axis of the quarter-wave plate. In FIG. 20, letter "a" indicates
that the crystal optic axis of the quarter-wave plate is at the normal
angular position of -45 degrees. Letter "b" indicates that the crystal
optic axis of the quarter-wave plate 11 is at the angular position of -30
degrees. Letter "c" indicates that the crystal optic axis of the
quarter-wave plate 11 is at the angular position of -15 degrees. Letter
"d" indicates that the crystal optic axis of the quarter-wave plate 11 is
at the angular position of 0 degrees. Letter "e" indicates that the
crystal optic axis of the quarter-wave plate 11 is at the angular
position of +15 degrees. Letter "f" indicates that the crystal optic axis
of the quarter-wave plate 11 is at the angular position of +30 degrees.
Letter "g" indicates that the crystal optic axis of the quarter-wave
plate is at the normal angular position of +45 degrees. In addition,
similar to FIG. 19, the horizontal axis indicates the angular position
(degrees) of the crystal optic axis of the half-wave plate 10, and the
vertical axis indicates the output of the polarization monitor 50.

[0188] FIG. 21 is a graph showing the changes in output contrast of the
polarization monitor at various angular positions of the crystal optic
axis of the quarter-wave plate. In FIG. 21, the horizontal axis indicates
the angular position (degrees) of the crystal optic axis of the
quarter-wave plate 11, and the vertical axis indicates the output color
contrast (contrast of the changes in the Stokes parameter S1 component)
of the polarization monitor 50. The output contrast at each angular
position of the crystal optic axis of the quarter-wave plate 11, for
example, is a value defined using the maximum and minimum values of the
curves showing the output changes indicated by letters a-g in FIG. 20 and
by an equation contrast=(maximum value-minimum value)/(maximum
value+minimum value).

[0189] The elliptically polarized light incident to the quarter-wave plate
11 is converted to linearly polarized light when the crystal optic axis
of the quarter-wave plate 11 is set such that the output contrast becomes
largest in FIG. 21. Therefore, in the adjustment method of this
embodiment, the angular position of the crystal optic axis of the
quarter-wave plate 11, at which the output contrast becomes largest (the
angular position of +30 degrees according to FIG. 21), is determined as
the desired first angular position for converting elliptically polarized
light into linearly polarized light, by referring to the changes in the
output contrast of the polarization monitor 50 at each angular position
of the crystal optic axis of the quarter-wave plate 11 (S14).

[0190]FIG. 22 is a graph showing the changes in the output of the
polarization monitor at various angular positions of the crystal optic
axis of the half-wave plate when the crystal optic axis of the
quarter-wave plate is fixed at the first angular position, which is for
converting elliptically polarized light into linearly polarized light. In
FIG. 22, the horizontal axis indicates the angular position (degrees) of
the crystal optic axis of the half-wave plate 10, and the vertical axis
indicates the output of the polarization monitor 50. If the crystal optic
axis of the half-wave plate 10 is configured such that the output of the
polarization monitor 50 becomes the maximum or minimum in FIG. 22,
linearly polarized light incident to the half-wave plate 10 is converted
to linearly polarized light having V-polarization (vertical polarization)
or H-polarization (horizontal polarization).

[0191] In the adjustment method of this embodiment, by referring to the
changes in the output of the polarization monitor 50 at various crystal
optic axes of the half-wave plate 10 when the crystal optic axis of the
quarter-wave plate 11 is fixed at the first angular position, the angular
position of the crystal optic axis of the half-wave plate 10 at the time
when the output of the polarization monitor becomes maximum or minimum
(angular position of -17.5 or +27.5 degrees or adjacent thereto according
to FIG. 22) is determined as the desired second angular position for
converting the incident linearly polarized light into linearly polarized
light having V- or H-polarization (S15).

[0192] Finally, the control system 70, via the drive system 71, adjusts
the angular position of the crystal optic axis of the quarter-wave plate
11 at the first angular position for converting the incident elliptically
polarized light into linearly polarized light, and the angular position
of the crystal optic axis of the half-wave plate 10 at the second angular
position for converting the incident linearly polarized light into the
linearly polarized light (e.g., V- or H-polarization) that has a
polarized plane in the predetermined direction (S 16). Because the
above-described first and second angular positions may change in response
to changes in illumination conditions (changes in the shape or size of
the light intensity distribution formed on the pupil plane of the
illumination optical system or adjacent thereto), it is preferable to
reset the crystal optic axes of the quarter-wave plate 11 and the
half-wave plate 10 as needed. In the above embodiment, the quarter-wave
plate and the half-wave plate are used for the polarized state switching
device. However, two quarter-wave plates may be used for the polarized
state switching device.

[0193] The above explanations are based on an exposure apparatus equipped
with an illumination optical system in which an illumination pupil
distribution forming device for forming a predetermined light intensity
distribution on the pupil plane or adjacent thereto based on the light
beam from a light source as shown in FIG. 1 or 16 includes two
diffractive optical elements (4, 6). However, this invention is not
limited to the structures shown in FIG. 1 or 16. There are various
modifications for the structures of illumination optical systems to which
this invention may be applied. FIG. 23 is a diagram schematically showing
a structure of an exposure apparatus that has an illumination pupil
distribution forming device having a structure different from ones shown
in FIG. 1 or 16.

[0194] The exposure apparatus according to the exemplary modification
shown in FIG. 23 has a structure similar to that for the exposure
apparatus shown in FIG. 16. However, the structures of the illumination
pupil distribution forming device, that is, the structure between the
diffractive optical element and the micro lens array 8 is different. The
structure and functions of the exemplary modification shown in FIG. 23
are described below, focusing on the difference from the exposure
apparatus shown in FIG. 16. In the exposure apparatus according to the
exemplary modification shown in FIG. 23, the light beam that is
transmitted through the diffractive optical element 4a for annular
illumination, for example, enters an afocal lens (relay optical system)
85. The afocal lens 85 is an afocal system (afocal optical system)
configured such that the position of a front focal point and the position
of the diffractive optical element 4a substantially match each other, and
such that the position of a rear focal point and the position of a
predetermined plane 86 shown by dotted lines in the figure substantially
match each other.

[0195] Therefore, a light beam with substantially parallel light rays that
enters the diffractive optical element 4a exits from the afocal lens as a
light beam with substantially parallel light rays after forming an
annular light intensity distribution on the pupil plane of the afocal
lens 85. On the pupil or adjacent thereto in the light path between a
front lens group 85a and a rear lens group 85b of the afocal lens 85, a
conical axicon system 87, a first cylindrical lens pair 88, and a second
cylindrical lens pair 89 are positioned in order from the light source
side. The detailed structure and functions thereof will be described
later. The basic structure and functions are described below, without
reference to the functions of the conical axicon system 87, the first
cylindrical lens pair 88, and the second cylindrical lens pair 89 to
simplify the explanations.

[0196] The light beam transmitted through the afocal lens 85 enters the
micro lens array 8, which functions as an optical integrator, through a
zoom lens (variable power optical system) for varying the σ value.
The predetermined plane 86 is positioned adjacent to the front side focal
point of the zoom lens 90. The incident surface of the micro lens array 8
is positioned adjacent to the rear focal point of the zoom lens 90. In
other words, the zoom lens 90 positions the predetermined plane 86 and
the incident surface of the micro lens array 8 in a substantial Fourier
transform relationship and thus positions the pupil plane of the afocal
lens 85 and the incident surface of the micro lens array 8 substantially
in optical conjugation. Therefore, similar to the pupil plane of the
afocal lens 85, on the incident surface of the micro lens array 8, an
annular illumination field about the optical axis AX, for example, is
formed. The total shape of the annular illumination field varies
similarly depending on the focal length of the zoom lens 90.

[0197] Each micro lens forming the micro lens array 8 has a rectangular
cross section similar to the shape of the illumination field to be formed
on the mask M (and thus the shape of the exposure region to be formed on
the wafer W). The light beam that enters the micro lens array 8 is
two-dimensionally divided by the large number of micro lenses. On the
rear focal plane (and thus the illumination pupil) is formed a secondary
light source having a light intensity that is substantially the same as
the illumination field formed by the light beam incident to the micro
lens array 8, that is, a secondary light source formed by a substantial
planar light source in an annular shape about the optical axis AX.

[0198] FIG. 24 is a diagram schematically showing the structure of the
conical axicon system provided in the light path between the front and
rear lens groups of the afocal lens shown in FIG. 23. The conical axicon
system 87 is structured from, in order from the light source side, the
first prism member 87a, having a flat surface that faces to the light
source side and a concave conical refractive surface that faces to the
mask side, and the second prism member 87b, having a flat surface that
faces to the mask side and a convex conical refractive surface that faces
to the light source side.

[0199] The concave conical refractive surface of the first prism member
87a and the convex conical refractive surface of the second prism member
87b are formed complementarily so as to be contactable to each other. In
addition, at least one of the first prism member 87a and the second prism
member 87b is structured so as to be movable along the optical axis AX so
that the space between the concave conical refractive surface of the
first prism member 87a and the convex conical refractive surface of the
second prism member 87b is variable.

[0200] When the concave conical refractive surface of the first prism
member 87a and the convex conical refractive surface of the second prism
member 87b are in contact with each other, the conical axicon system 87
functions as a plane parallel plate. Therefore, the annular secondary
light source formed is not affected. However, when the concave conical
refractive surface of the first prism member 87a and the convex conical
refractive surface of the second prism member 87b are separated, the
conical axicon system 87 functions as a so-called beam expander.
Therefore, the angle of the light beam incident to the predetermined
plane 86 varies in accordance with the changes of the space in the
conical axicon system 87.

[0201] FIG. 25 is a diagram that explains functions of the conical axicon
system with respect to the secondary light source formed in annular
illumination in the exemplary modification shown in FIG. 23. In the
annular illumination in the exemplary modification shown in FIG. 23, by
increasing the space in the conical axicon system 87 from zero to a
predetermined value, the smallest annular secondary light source 130a,
which is formed when the space in the conical axicon system 87 is zero
and when the focal length of the zoom lens 90 is set at the smallest
value (hereinafter referred as "normal state"), is changed to an annular
secondary light source 130b, of which both outer and inner diameters are
expanded, without changing the width (1/2 of the difference between the
outer and inner diameters as indicated by arrows). In other words, the
annular ratio (inner diameter/outer diameter) and the size (outer
diameter) are both changed by the operation of the conical axicon system
87 without changing the width of the annular secondary light source.

[0202] FIG. 26 is a diagram explaining the function of the zoom lens with
respect to the secondary light source formed in the annular illumination
in the exemplary modification shown in FIG. 23. In the annular
illumination in the exemplary modification shown in FIG. 23, the annular
secondary light source 130a formed in the normal state is changed to an
annular secondary light source 130c, having a total shape that is
expanded similarly by expanding the focal length of the zoom lens 90 from
the smallest value to a predetermined value. In other words, both the
width and the size (outer diameter) of the annular secondary light source
are changed by the operation of the zoom lens 90 without changing the
annular ratio.

[0203] FIG. 27 is a diagram schematically showing a structure of the first
and second cylindrical lens pairs provided in the light path between the
front and rear lens groups of the afocal lens shown in FIG. 23. In FIG.
27, the first cylindrical lens pair 88 and the second cylindrical lens
pair 89 are provided in order from the light source side. The first
cylindrical lens pair 88 is structured by, from the light source side,
the first cylindrical negative lens 88a having negative refractive power
in the YZ plane and no refractive power in the XY plane, and the first
cylindrical positive lens 88b having positive refractive power in the YZ
plane and no refractive power in the XY plane, for example.

[0204] On the other hand, the second cylindrical lens pair 89 is
structured by, from the light source side, the second cylindrical
negative lens 89a having negative refractive power in the XY plane and no
refractive power in the YZ plane, and the second cylindrical positive
lens 89b having the positive refractive power in the XY plane and no
refractive power in the YZ plane, for example. The first cylindrical
negative lens 88a and the first cylindrical positive lens 88b are
structured so as to be integrally rotatable about the optical axis AX.
Similarly, the second cylindrical negative lens 89a and the second
cylindrical positive lens 89b are structured so as to be integrally
rotatable about the optical axis AX.

[0205] Accordingly, in a state shown in FIG. 27, the first cylindrical
lens pair 88 functions as a beam expander having power in the Z
direction, and the second cylindrical lens pair 89 functions as a beam
expander having power in the X direction. In the exemplary modification
shown in FIG. 23, the power for the first cylindrical lens pair 88 and
the power for the second cylindrical lens pair 89 are set to be the same.

[0206] FIGS. 28-30 are diagrams explaining the operation of the first and
second cylindrical lens pairs with respect to the secondary light source
formed in the annular illumination in the exemplary modification shown in
FIG. 23. In FIG. 28, the direction of the power of the first cylindrical
lens pair 88 is set to form an angle of +45 degrees from the Z axis about
the optical axis AX, and the direction of the power of the second
cylindrical lens pair 89 is set to form an angle of -45 degrees from the
Z axis about the optical axis AX.

[0207] Therefore, the directions of the power of the first cylindrical
lens pair 88 and the second cylindrical lens pair 89 intersect at right
angles to each other, and the power in the Z direction and the power in
the X direction become the same in a combined system of the first
cylindrical lens pair 88 and the second cylindrical lens pair 89. As a
result, in a perfect circle state shown in FIG. 28, the light beam that
is transmitted through the combined system of the first cylindrical lens
pair 88 and the second cylindrical lens pair 89 is expanded with the same
power in the Z and X directions. Therefore, a perfect annular secondary
light source is formed on the illumination pupil.

[0208] In FIG. 29, the direction of the power of the first cylindrical
lens pair 88 is set to form an angle of +80 degrees, for example, with
respect to the Z direction about the optical axis AX, and the direction
of the power of the second cylindrical lens pair 89 is set to form an
angle of -80 degrees, for example, with respect to the Z direction about
the optical axis AX. Therefore, the power in the X direction becomes
larger than the power in the Z direction in the combined system of the
first cylindrical lens pair 88 and the second cylindrical lens pair 89.
As a result, in a horizontally elliptical state shown in FIG. 29, the
light beam that is transmitted through the combined system of the first
cylindrical lens pair 88 and the second cylindrical lens pair 89 is
expanded with larger power in the X direction than in the Z direction.
Therefore, a horizontally long annular secondary light source that is
elongated in the X direction is formed on the illumination pupil.

[0209] In FIG. 30, the direction of the power of the first cylindrical
lens pair 88 is set to form an angle of +10 degrees, for example, with
respect to the Z direction about the optical axis AX, and the direction
of the power of the second cylindrical lens pair 89 is set to form an
angle of -10 degrees, for example, with respect to the Z direction about
the optical axis AX. Therefore, the power in the Z direction becomes
larger than the power in the X direction in the combined system of the
first cylindrical lens pair 88 and the second cylindrical lens pair 89.
As a result, in a vertically elliptical state shown in FIG. 30, the light
beam that is transmitted through the combined system of the first
cylindrical lens pair 88 and the second cylindrical lens pair 89 is
expanded with larger power in the Z direction than in the X direction.
Therefore, a vertically long annular secondary light source that is
elongated in the Z direction is formed on the illumination pupil.

[0210] Further, by setting first cylindrical lens pair 88 and the second
cylindrical lens pair 89 in any state between the perfect circular state
shown in FIG. 28 and the horizontally elliptical state shown in FIG. 29,
horizontally annular secondary light sources in accordance with various
vertical/horizontal ratios can be formed. In addition, by setting first
cylindrical lens pair 88 and the second cylindrical lens pair 89 in any
state between the perfect circular state shown in FIG. 28 and the
vertically elliptical state shown in FIG. 30, vertically annular
secondary light sources in accordance with various vertical/horizontal
ratios can be formed. In the exemplary modification shown in FIG. 23,
circular illumination and various modified illuminations may be achieved
by setting a diffractive optical element for the circular illumination or
a diffractive optical element for multi-pole (e.g., quadrupole)
illumination, instead of the diffractive optical element 4a for annular
illumination. Therefore, in the exemplary modifications shown in FIGS.
23-30, the polarized state for the illumination light can be changed in
accordance with the pattern characteristics of the mask M, and the
vertical/horizontal ratio of the secondary light source formed on the
illumination pupil may be adjusted as needed. As such, excellent exposure
may be performed with an appropriate illumination condition achieved in
accordance with the pattern characteristics of the mask M.

[0211] In addition, in each of the above-described embodiments and
exemplary modifications, if there are fluctuations in uneven illumination
on the illuminated surface, fluctuations in the light intensity
distribution on the pupil plane, and/or fluctuations in telecentricity on
the illuminated surface when switching between the linearly polarized
state and the nonpolarized state or between the X-polarized state and the
Y-polarized state, it is preferable to reduce the fluctuations in the
uneven illumination, the fluctuations in the light intensity distribution
on the pupil plane, and/or the fluctuations in the telecentricity by
controlling the uneven illumination, the light intensity distribution on
the pupil plane and/or the telecentricity in accordance with the changes
in the polarized state on the illuminated surface.

[0212] For example, the uneven illumination on the illuminated surface can
be controlled by changing the lens position and orientation of at least a
part of the plurality of lens elements forming the condenser optical
system 9 shown in FIG. 1 or the condenser optical system 9a shown in FIG.
16 or 23. In addition, in the light path between the condenser optical
system 9 and the mask M shown in FIG. 1 or in the light path between the
condenser optical system 9 and the mask blind MB shown in FIG. 16 or 23,
a density filter plate disclosed in Japanese Laid-Open Patent Application
No. 2002-100561 (and corresponding U.S. Patent Publication No.
2003/0025890A, which is incorporated herein by reference in its entirety)
or disclosed in Japanese Laid-Open Patent Application No. 2003-92253 (and
corresponding U.S. Patent Publication No. 2003/0067591A. which is
incorporated herein by reference in its entirety) may be positioned. By
controlling rotational angle and position of the density filter plate,
the uneven illumination on the illuminated surface can be controlled.
Moreover, instead of or in the proximity of the mask blind MB shown in
FIG. 16 or 23, a variable blade disclosed by Japanese Laid-Open Patent
Application No. 2002-184676, for example, may be provided. The uneven
illumination on the illuminated surface can also be controlled by setting
the variable blade such that the width of the exposure region in the
scanning direction may be different from that in the non-scanning
direction.

[0213] Furthermore, the light intensity distribution on the pupil plane
can be controlled by positioning the density filter plate disclosed in
the above Japanese Laid-Open Patent Application No. 2002-100561 (U.S.
Patent Publication No. 2003/0025890A) and Japanese Laid-Open Patent
Application No. 2003-92253 (U.S. Patent Publication No. 2003/0067591A)
adjacent to the illumination pupil, such as adjacent to the exit side of
the micro lens array 8.

[0214] The telecentricity can be controlled by changing the lens position
and orientation of at least a part of the plurality of lens elements
forming the condenser optical system 9 shown in FIG. 1 or the condenser
optical system 9a shown in FIG. 16 or 23.

[0215] In addition, by pre-calculating the relationships between the
configuration of the polarized state switching device (insertion/removal
of the depolarizer, a rotational angle of the half-wave plate, and a
rotational angle of the quarter-wave plate) and the condition of the
uneven illumination on the illuminated surface, the light intensity
distribution on the pupil plane and the telecentricity, the uneven
illumination on the illuminated surface, the light intensity distribution
on the pupil plane and the telecentricity can be controlled in accordance
with the configuration of the polarized state switching device.
Furthermore, by measuring the uneven illumination on the illuminated
surface, the light intensity distribution on the pupil plane, and the
telecentricity on the illuminated surface or a surface optically
conjugate to the illuminated surface, the uneven illumination on the
illuminated surface, the light intensity distribution on the pupil plane,
and the telecentricity may also be controlled in accordance with the
result of the measurement.

[0216] In the above-described embodiments and exemplary modifications, the
micro lens array 8, which is formed by a plurality of micro lenses having
positive refractive power densely arranged in a matrix, is used as an
optical integrator. However, instead of the micro lens array 8, a
cylindrical micro lens array, which has a first one-dimensional
cylindrical lens array arranged in a pitch along a predetermined first
direction and a second one-dimensional cylindrical lens array arranged in
a pitch along a second direction orthogonal to the first direction, may
be used. It is preferable that the first and second one-dimensional
cylindrical lens arrays of the cylindrical micro lens array are provided
integrally with a single light transmissive substrate, and more
particularly preferable that a plurality of cylindrical lens array plates
having the first and second one-dimensional cylindrical lens arrays are
provided and positioned spaced from each other along the direction of the
optical axis. In addition, it is preferable that at least one of the
pitch of the first one-dimensional cylindrical lens array in the first
direction and the pitch of the second one-dimensional lens array in the
second direction is less than 2 mm.

[0217] With this structure, unlike the ordinary fly's-eye lens, for which
each refractive surface is formed in two-dimensional curvature (spherical
shape), each refractive surface of the first and second one-dimensional
cylindrical lens arrays of the cylindrical micro lens array is formed in
one-dimensional curvature (cylindrical shape). Therefore, highly
precision processes become easy, and thus, the manufacturing cost may be
decreased. In particular, for the cylindrical micro lens array, in which
the smallest pitch is 2 mm or less, the reduction in the manufacturing
cost is significant. In addition, such a cylindrical micro lens array can
be manufactured by grinding, etching, and/or tool-pressing processes.

[0218] By use of a cylindrical micro lens array that is highly precise in
shape and manufactured at low cost, illumination with excellent
uniformity may be achieved. Therefore, in combination with an enormous
improvement in image forming characteristics using polarized
illumination, micro patterns may be formed with high transfer accuracy
throughout the entire exposure regions.

[0219] A cylindrical micro lens array is proposed in the specification and
drawings of Applicant's Japanese Patent Application No. 2002-152634 (and
corresponding U.S. Patent Publication No. 2004/0036977A). The present
specification incorporates by reference the disclosure of U.S. Patent
Publication No. 2004/0036977A in its entirety.

[0220] In the exposure apparatus according to the above-described
embodiments, micro devices (semiconductor elements, imaging elements,
liquid crystal display elements, thin film magnetic heads, etc.) may be
manufactured by illuminating a mask (reticle) by an illumination optical
system and exposing a transfer pattern formed on the mask onto a
photosensitive substrate using a projection optical system. An exemplary
method for obtaining a semiconductor device, as the micro device, by
forming a predetermined circuit pattern on a wafer or the like, as the
photosensitive substrate, using the exposure apparatus according to the
above-described embodiments is explained below with reference to a flow
chart shown in FIG. 12.

[0221] First, in step 301 in FIG. 12, a metallic film is vapor-deposited
on the wafers of one lot. In next step 302, photoresist is applied onto
the metallic film on the wafers of one lot. Thereafter, in step 303,
using the exposure apparatus of the above-described embodiments, an image
of a pattern on a mask is sequentially exposed and transferred onto each
shot region on the wafers of one lot through a projection optical system.
Then, after the photoresist on the wafers of one lot is developed in step
304, by etching the resist pattern on the wafers of one lot as a mask, a
circuit pattern corresponding to the pattern on the mask is formed in
each shot region on each wafer in step 305. By forming a circuit pattern
on an upper layer, for example, a device such as a semiconductor device
can be manufactured. According to the above-described method for
manufacturing semiconductor devices, the semiconductor devices having an
extremely micro circuit pattern may be obtained at good throughput.

[0222] Furthermore, in the exposure apparatus of the above-described
embodiments, liquid crystal display elements may be obtained as the micro
device by forming a predetermined pattern (circuit pattern, electrode
pattern, etc.) on a plate (glass substrate). An exemplary method is
explained below with reference to a flow chart shown in FIG. 13. In FIG.
13, in a pattern formation step 401, a so-called photolithography process
is performed, in which a mask pattern is transferred and exposed onto a
photosensitive substrate (a glass substrate or the like applied with
resist) using the exposure apparatus in the above-described embodiments.
By this photolithography process, a predetermined pattern that may
include a large number of electrodes or the like is formed on the
photosensitive substrate. Thereafter, the predetermined pattern is formed
on the substrate as the exposed substrate proceeds with developing,
etching, and resist removal processes. Then, the color filter formation
step 402 is performed.

[0223] Next, in the color filter formation step 402, a color filter is
formed, in which a large number of groups of three dots corresponding to
R (red), G (green) and B (blue) is arranged in a matrix, or in which a
plurality of groups of three strip filters corresponding to R, G and B,
is arranged in the horizontal scan line direction. Then, after the color
filter formation step 402, a cell assembly step 403 is performed. In the
cell assembly step 403, a liquid crystal panel (liquid crystal cell) is
assembled using the substrate having the predetermined pattern that is
obtained in the pattern formation step 401 and the color filter obtained
in the color filter formation step 402,

[0224] In the cell assembly step 403, the liquid crystal panel (liquid
crystal cell) is manufactured by, for example, injecting liquid crystal
material between the substrate having the predetermined pattern that is
obtained in the pattern formation step 401 and the color filter obtained
in the color filter formation step 402. Then, in a module assembly step
404, various parts, such as an electric circuitry and a backlight, that
perform display operation for the assembled liquid crystal panel (liquid
crystal cell) and provided to complete the process. According to the
above-described method for manufacturing liquid crystal display elements,
liquid crystal display elements having extremely micro circuit patterns
can be obtained with good throughput.

[0225] In the embodiment shown in FIG. 1, the mask is illuminated
superimposingly by collecting the light from the secondary light source
by the condenser optical system 9. However, this invention is not limited
to this. As shown in the exemplary modification shown in FIG. 16, an
illumination field diaphragm (mask blind) and a relay optical system that
forms an image of the illumination field diaphragm on the mask M may be
arranged in the light path between the condenser optical system 9 and the
mask M. In this case, the condenser optical system 9 illuminates the
illumination field diaphragm superimposingly by collecting the light from
the secondary light source. Therefore, the relay optical system forms on
the mask M an image of an opening (light transmissive part) of the
illumination field diaphragm.

[0226] Furthermore, in the above-described embodiments, KrF excimer laser
light (wavelength: 248 nm) or ArF excimer laser light (wavelength: 193
nm) is used as the exposure light. However, the invention is not limited
to this. This invention may be applied to other appropriate laser light
sources, such as an F2 laser light source that provides laser light
at a wavelength of 157 nm, and light sources other than laser light
sources, such as a lamp light source that provides ultraviolet light,
such as i-line, g-line and h-line. Moreover, in the above-described
embodiments, this invention is explained with respect to a projection
exposure apparatus equipped with an illumination optical system as an
example. However, this invention may be applied to a general illumination
optical system for illuminating an illuminated surface other than a mask.

[0227] In addition, in the above-described embodiment, a so-called
immersion method is used, in which the light path between the projection
optical system and the photosensitive substrate is filled with a medium
(typically liquid) having a refractivity greater than 1.1. In this case,
as the method that fills the light path between the projection optical
system and the photosensitive substrate with liquid, a method disclosed
in International Publication No. WO99/49504 that locally fills with
liquid, a method disclosed in Japanese Laid-Open Patent Application No.
6-124873 that moves a stage holding a substrate that is the object of
exposure in a liquid tank, and a method disclosed in Japanese Laid-Open
Patent application Ser. No. 10-303114 that forms a liquid tank having a
predetermined depth on a stage and holds a substrate therein, may be
used. The disclosure of WO99/49504 is incorporated herein by reference in
its entirety.

[0228] As the liquid, it is preferable to use one that has transmissivity
for the exposure light, has a high refractivity, and is stable for a
photoresist applied on the projection optical system and/or substrate.
For example, purified water and deionized water may be used when KrF
excimer laser light or ArF excimer laser light is used as the exposure
light. Moreover, fluorinated liquid, such as fluorinated oil or
fluoropolyether (PFPE), which can transmit F2 laser light, may be
used as the liquid when the F2 laser light is used as the exposure
light.

[0229] Furthermore, this invention may be used in a twin-stage type
exposure apparatus disclosed in Japanese Laid-Open Patent Application
Nos. 10-163099 and 10-214783 (and corresponding U.S. Pat. No. 6,400,441,
the disclosure of which is incorporated herein by reference in its
entirety), and PCT Publication No. 2000-505958 (and corresponding U.S.
Pat. No. 5,969,441, the disclosure of which is incorporated herein by
reference in its entirety), which provides two stages that hold processed
substrates, such as wafers, separately and are independently movable in
the XY directions.

[0230] As described above, in the illumination optical system of this
invention, the polarized state of the light that illuminates the
illuminated surface may be switched between a specified polarized state
(e.g., linearly polarized state) and nonpolarized state by the function
of the polarized state switching device structured from a half-wave plate
and a depolarizer (nonpolarized element). Therefore, when the
illumination optical system of this invention is installed an exposure
apparatus, for example, excellent illumination conditions can be achieved
by changing the polarized state of the illumination light while
controlling the loss of light amount in accordance with the
characteristics of mask patterns.

[0231] Moreover, in the exposure apparatus that uses the illumination
optical system and exposure method of this invention, because excellent
illumination conditions may be achieved by changing the polarized state
of the illumination light in accordance with the characteristics of the
pattern on the mask M, excellent exposure can be performed under the
excellent illumination conditions achieved in accordance with the
characteristics of the patterns on the mask M. Therefore, excellent
devices at a high throughput can be manufactured.

[0232] While the invention has been described with reference to preferred
embodiments thereof, it is to be understood that the invention is not
limited to the preferred embodiments or constructions. The invention is
intended to cover various modifications and equivalent arrangements. In
addition, while the various elements of the preferred embodiments are
shown in various combinations and configurations, that are exemplary,
other combinations and configurations, including more, less or only a
single element, are also within the spirit and scope of the invention.

Patent applications by Hirohisa Tanaka, Kumagaya-Shi JP

Patent applications by Hisashi Nishinaga, Tokima JP

Patent applications by Kenichi Muramatsu, Sagamihara-Shi JP

Patent applications by Norio Komine, Sagamihara-Shi JP

Patent applications by Osamu Tanitsu, Kumagaya-Shi JP

Patent applications by Takehito Kudo, Kumagaya-Shi JP

Patent applications by Tomoyuki Matsuyama, Korihashi-Machi JP

Patent applications by NIKON CORPORATION

Patent applications in class Including shutter, diaphragm, polarizer or filter

Patent applications in all subclasses Including shutter, diaphragm, polarizer or filter